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S 
CONNECTICUT  nOvl^? 


AGEICDlieESL  EXPERIMENT  STillOIi 

NEW^    HAVEN,    CONN.        • 


BULLETIN   158,  NOVEMBER,    1907. 


The  Relation  of  Certain  Biological  Principles 
to  Plant  Breeding. 


BY 

EDWARD  M.   EAST,   Ph.D. 


The  Bulletins  of  this  Station  are  mailed  free  to  citizens  of  Con- 
necticut who  apply  for  them,  and  to  others  as  far  as  the  editions 
permit. 


COSHECTICnT  A&RICDLTnEAL  EIPEBIMENT  STATION, 


BOARD   OF   CONTROL. 
His  Excellency,  Rollin  S.  Woodruff,  Ex  officio,  President. 

Prof.  H.  W.  Conn  Middletown. 

Prof.  W.  H.  Brewer,  Secretary  New  Haven. 

B.  W.  Collins Meriden. 

Charles  M.  Jarvis  Berlin. 

Edwin  Hoyt   New  Canaan. 

J.  H.  Webb Hamden. 

E.  H.  Jenkins,  Director  and  Treasurer New  Haven. 


STATION    STAFF. 

Chemists. 

Analytical  Laboratory. 

John  P.  Street,  M.S.,  Chemist  in  Charge. 

E.  Monroe  Bailey,  M.S.  C.  B.  Morrison,  B.S. 

H.  R.  Stevens,  B.S. 

Laboratory  for  the  Study  of  Proteids. 

T.  B.  Osborne,  Ph.D.,  Chemist  in  Charge.       C.  A.  Brautlecht,  Ph.B. 

Botanist. 
G.  P.  Clinton,  S.D. 

Entomologist. 
W.  E.  Britton,  Ph.D. 

Assistant  in  Entomology. 
B.  H.  Walden,  B.Agr. 

Forester. 
Austin  F.  Hawes,  M.F. 

Agronomist. 
Edward  M.  East,  Ph.D. 

Stenographers  and  Clerks. 

Miss  V.  E.  Cole. 
Miss  L.  M.  Brautlecht. 
Miss  E.  B.  Whittlesey. 

In  charge  of  Buildings  and  Grounds. 
William  Veitch. 

Laboratory  Helpers. 

Hugo  Lange. 

c.  d.  hubbell. 

Sampling  Agent. 
V.  L.  Churchill,  New  Haven. 


TABLE  OF  CONTENTS. 


Introduction. 

I.  The  Evolution  of  Darwin  and  his  Predecessors.  7 

Lamarckism. 

The  theory — Its  foundations — The  meagre  experimental 
evidence — Modification  due  to  environment — Temporary 
inheritance  of  modifications — Weismann's  theory. 

Darwinism. 

The  Malthusian  doctrine — Survival  of  the  fittest — Evidences 
of  evolution — Organic  relationship — Geographical  distribu- 
tion— Geological  evidence — Comparative  structures — Embry- 
ological  evidence — ^Variation  under  domestication — Sum- 
mary— Post-Darwinian  questions. 

II.  Later  Evolutionary  Theories  and  Principles.  20 
Criticisms  of  Darwin's  mechanical  theory. 

Variation — Classes  of — Darwin's  belief  in  evolution  through 
fluctuations — Early    criticisms    of    this    view — Recent    criti- 
cisms— De  Vries'   experimental   evidence  against — Evidence 
of  biometry  against — ^Johannsen's  work — Conclusion. 
The  mutation  theory. 

Introductory — Linnaeus'  vs.  Jordan's  species — Elementary 
species — Unit  characters — The  theory — The  primrose  experi- 
ments— The  chief  points  concerning  mutations — Kinds  of 
mutations — Nature  of  mutation. 

III.  Heredity.  36 
Introduction. 

Blended  inheritance. 

Examples — Prepotency. 
Mosaic  inheritance. 
Alternate  inheritance  and  Mendelism. 

Definition — Mendel — His  experiments  with  a  single  pair  of 

characters — His  results — His  theory — Results  with  two  pairs 

of  characters — General  law — Conclusion. 

IV.  Methods  of  Plant  Improvement.  45 
Introduction — The  three  methods. 

The  selection  of  fluctuations. 

The  sugar  beet — Maize  breeding  to  change  the  composition 
of  the  kernels — Inconstancy  of  races  improved  by  fluctua- 
tions— Propagating  extreme  fluctuations  by  asexual  means. 


4  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    1 58. 

Isolation  of  elementary  species. 

Le  Couteur — Patrick  Shirreff — Nilsson — Types  found  in 
clover — What  the  types  are — Distinctions  between  selecting 
fluctuations  and  isolating  elementary  species — Judging  plants 
by  their  progeny — Correlated  characters — Definitions — Ex- 
amples— Nilsson's  work — The  Primus  barley. 

Improvement  by  hybridization. 

Definition  —  Fairchild  —  Kolreuter  —  Reciprocal  crosses  — 
Knight — Cause  of  variation — ^Knight-Darvvin  law — Rela- 
tionships and  crosses — Prepotency  of  pollen — Later  Men- 
delian  work — Morgan's  hypothesis  of  germ  cell  dominance — 
Bateson's  presence  and  absence  hypothesis — Masked  char- 
acters— Reversion — Heterozygotes — Practical  applications  of 
Mendel's  law — Conclusion. 
V.    Technique  in  Plant  Breeding.  T2> 

Introduction. 

Flowers  and  their  parts. 

Technique  of  hybridizing. 

Sexual  habits  of  the  plant — maturity  of  the  pollen — 
Maturity  of  the  stigma — Prevention  of  accidental  pollina- 
tion— Keeping  pollen. 

Technique  of   isolating  elementary  species. 

Habits  of  the  subject  plants — The  pedigree  culture  illus- 
trated by  red  clover — Elementary  species  that  have  been 
found. 

Technique  of  maize  breeding. 

The  problem — Early  history — The  row  system — Standard 
rows — Dangers  of  inbreeding — The  Illinois  system — Criti- 
cism— The  Ohio  system — Criticism — A  suggested  method — 
The  theoretical  foundation  of  methods. 

Conclusion.  89 


THE  RELATION  OP  CERTAIN  BIOLOGICAL  PRINCIPLES 
TO  PLANT  BREEDING. 

By  EDWARD  M.  EAST. 


Introductiox 

The  recent  stupendous  progress  in  the  experimental  study  of 
variation,  evolution  and  heredity  has  awakened  greater  interest 
in  the  improvement  of  cultivated  crops,  for  the  theory  of  the 
two  studies  must  inevitably  go  together.  Since  the  publication 
of  the  Origin  of  Species  in  1859,  the  questions  involved  have 
been  much  at  the  mercy  of  the  speculations  of  theorists ;  and  it 
was  seemiiigly  forgotten  that  Darwin  himself  obtained  much  of 
his  evidence  from  domestic  animals  and  cultivated  plants.  The 
theorists  were  too  busy  in  their  debates  to  obtain  many  results 
of  practical  value  to  the  plant  breeders;  and  the  plant  breeders 
were  obtaining  so  many  surprising  complications  in  their  experi- 
mental work,  that  the  thought  of  the  possibility  of  classifying 
their  thousands  of  observations  under  a  few  natural  laws  did 
not  occur  to  them. 

The  last  decade  has  brought  about  a  change  of  heart  in  the 
two  classes  of  workers,  and  a  change  in  method  in  their  work. 
The  student  of  natural  evolution  and  the  follower  of  changes 
under  domestication  have  recognized  that  they  stand  upon  com- 
mon ground,  and  as  a  result,  the  brilliant  researches  of  a  score 
or  more  of  recent  investigators  have  made  the  prospects  of  gain 
in  the  practical  side  almost  too  alluring. 

For  the  plant  breeder  who  can  devote  his  whole  time  to  the 
study  of  his  immediate  problems,  who  will  prepare  himself  by  a 
study  of  former  investigations  concerning  variation  and  heredity, 
and  who  will  keep  his  ideas  abreast  of  modern  research,  the 
rewards  indicated  in  some  of  the  current  journals  are  hardly 
exaggerated.  But  for  the  busy  farmer  who  wishes  to  know  the 
best  methods  of  improving  his  general  farm  crops  there  is  need 
of  caution  in  accepting  the  promise  of  results.     Popular  articles 


6  CONNECTICUT   EXPERIMENT    STATION    BULLETIN    158. 

have  been  written  of  such  roseate  hue  that  large  numbers  of 
men  are  quite  ready  to  spend  a  portion  of  their  time  and  money 
in  the  improvement  of  their  favorite  crop.  The  general  feeling 
toward  plant  breeding  is  good  and  is  certain  to  be  productive 
of  valuable  results;  but  it  is  not  a  subject  from  which  to  expect 
great  things  without  the  study  necessary  for  a  general  apprecia- 
tion of  its  principles.  Most  certainly  the  writer  does  not  wish 
to  discourage  an  increase  in  the  number  already  interested  in 
plant  breeding,  but  to  encourage  a  greater  study  of  its  under- 
lying principles  and  to  have  a  rational  view  taken  of  our  present 
status  of  knowledge  as  to  the  possibilities  which  lie  within  the 
application  of  these  principles. 

The  prevalence  of  inadequate  preparation  for  undertaking 
special  problems  of  practical  plant  breeding  is  partially  due  to 
the  unavailability  of  collected  information  on  the  subject.  Com- 
pilation in  text-book  form  has  not  kept  pace  with  the  rapid 
increase  in  results  of  research.  There  is  disagreement  as  to 
detail  of  method  in  the  application  of  the  few  principles  which 
have  been  discovered  and  it  is  well  that  the  prospective  plant 
breeder  should  consider  these  principles  from  various  points  of 
view  and  draw  his  own  conclusions. 

There  will  be  given  in  the  following  pages  a  short  outline  of 
the  current  belief  in  the  most  important  theories  and  principles 
of  variation,  evolution  and  heredity,  with  their  practical  applica- 
tion to  methods  of  breeding  farm  crops,  which  it  is  hoped  will 
give  the  farmer  an  idea  of  the  scope  and  present  state  of  the 
problems.  Should  the  reader  be  sufficiently  interested  to  pursue 
the  subject  further^,  he  should  consult  the  annotated  list  of 
supplementary  reading  given  at  the  end  of  this  paper. 

In  the  preparation  of  this  paper,  the  writer  has  made  free  use 
of  the  works  of  the  following  writers: — Bailey,  Bateson,  Biffen, 
Castle,  Correns,  Darwin,  Davenport,  De  Vries,  Hurst,  Johannsen, 
Lock,  Kellogg,  Morgan,  Pearson,  Punnet,  Romanes,  Saunders, 
Shirreff,  Tschermak,  Vernon,  Webber,  Weismann  and  others, 
including  our  own  government  and  experiment  station  workers. 


EVOLUTION    OF   DARWIN    AND    HIS    PREDECESSORS. 


The  Evolution  of  Darwin  and  his  Predecessors. 

Lamarckism. 

The  idea  of  organic  evolution  had  germinated  in  the  minds  of 
a  number  of  deep  thinkers  from  the  time  of  Aristotle,  and  finally 
bore  fruit  in  the  overwhelming  evidence  presented  by  Charles 
Darwin  in  1859.  The  adoption  of  the  Jewish  idea  of  the  separate 
creation  of  species  by  the  Christian  churches  had  almost  stifled 
early  speculation.  However,  in  the  eighteenth  and  early  nine- 
teenth centuries,  we  find  a  more  or  less  definite  idea  of  the 
production  of  species  by  the  modification  of  their  progenitors, 
expressed  by  Erasmus  Darwin,  De  Maillet,  Goethe  and  Trevira- 
nus.  Lamarck  had  even  developed  a  well  rounded  theory  of  evo- 
lution through  the  inheritance  of  characters  acquired  during  the 
lives  of  individuals,  a  full  half  century  before  the  time  of  Darwin. 
The  underlying  thought  of  Lamarck's  theory  of  the  inheri- 
tance of  the  effect  of  use  and  disuse  may  be  seen  in  the  example 
which  he  himself  first  proposed  in  its  favor.  A  bird,  driven 
through  hunger  to  the  water  for  food,  will  instinctively  separate 
its  toes  when  they  strike  the  water.  The  skin  uniting  the  bases 
of  its  toes  will  be  stretched,  in  consequence.  By  the  continuation 
of  this  process,  the  descendants  of  such  birds  will  develop  the 
broad  membrane  possessed  by  water  birds  such  as  ducks  and 
geese. 

Lamarck's  arguments  may  be  given  in  a  summary  of  his  own 
which  is  often  quoted.  He  gives  it  as  two  laws  of  nature. 
First  law :  "In  every  animal  which  has  not  finished  its  term  of 
development,  the  frequent  and  sustained  use  of  any  organ 
strengthens  and  develops  it  and  increases  it  in  size  proportionate 
to  the  length  of  time  it  has  been  employed.  On  the  other  hand, 
the  continued  lack  of  use  of  any  organ  gradually  weakens  it 
until  at  last  it  disappears."  Second  law:  "Nature  preserves 
everything  she  has  caused  the  individual  to  acquire  or  lose 
through  the  influence  of  the  environment  to  which  its  race  has 
been  for  a  long  time  exposed,  and  henpe  the  predominance  or 
loss  of  certain  organs  through  use  or  disuse.  She  does  this  by 
the  production  of  new  individuals  which  are  endowed  with  the 


8  CONNECTICUT   EXPERIMENT    STATION    BULLETIN    153- 

newly  acquired  organs,  provided  the  acquired  changes  were 
common  to  the  two  sexes  of  the  individuals  that  produced  the 
new  forms." 

In  other  words,  Lamarck  has  explained  the  diverse  instances 
of  the  survival  of  certain  characters  useful  to  the  organism  by 
the  theory  that  the  need  of  such  characters  has  caused  their 
necessary  modification  through  the  inheritance  of  such  charac- 
ters partially  acquired  or  partially  lost  during  the  lifetime  of 
different  separate  individuals. 

Since  Darwin's  time,  the  principles  of  Lamarck,  with  some 
modifications,  have  received  warm  support  by  a  large  following 
of  eminent  scholars,  the  so-called  Neo-Lamarckian  school,  of 
which  Spencer,  Cope,  Eimer,  Hyatt,  Cunningham  and  Osborn 
are  a  few  of  the  well  known  writers  who  have  collected  data 
in  its  support.  It  is  noticeable  that  the  best  evidence  has  been 
advanced  by  paleontologists,  who  have  been  deeply  impressed  by 
the  direct  lines  of  evolution  that  geological  evidence  seems  to 
show  has  taken  place.  To  their  minds,  the  inheritance  of 
acquired  characters  must  have  taken  place,  to  give  a  sufficient 
explanation  of  these  facts. 

We  can  only  say  that  while  many  of  the  facts  seem  to  be 
reasonably  explained  by  the  theory,  the  crucial  point  of  the  whole 
thing,  which  is  actual  permanent  inheritance  of  an  acquired 
character,  has  not  been  shown.  It  is  true  that  this  definite  ques- 
tion has  been  attacked  by  but  few  experiments,  but  in  such  experi- 
ments the  results  have  been  negative.  Successive  generations  of 
mutilations,  such  as  docked  tails  of  horses,  have  never  resulted 
in  a  single  case  of  undisputed  inheritance.  The  idea  that 
previous  fecundations  have  an  effect  upon  succeeding  progeny 
of  a  mother  has  been  shown  to  be  without  foundation.  The 
allied  botanical  phenomenon  of  zenia,  as  illustrated  by  the  effect 
during  the  current  season  of  pollen  of  a  black  maize  upon  the 
endosperm  of  a  white  variety,  has  been  proved  to  have  another 
and  a  simple  explanation.  Thus  we  may  go  through  the  entire 
list. 

The  one  class  of  data  that  comes  the  nearest  toward  showing 
inheritance  of  body  acquirements,  is  that  of  the  modifica- 
tion of  certain  characters  by  the  immediate  influence  of  the 
factors  of  environment,  as  food,  light,  heat,  moisture,  etc.  In 
many   instances,    where   the    environment   of   plants    has    been 


EVOLUTION    OF   DARWIN    AND    HIS    PREDECESSORS.  9 

changed,  there  does  indeed  seem  to  be  a  temporary  inheritance 
of  certain  modifications.  For  instance,  various  grains  have  been 
taken  from  their  native  plains  and  transplanted  to  mountains  or 
high  plateaus.  Among  other  minor  changes  that  here  have 
taken  place  are  earlier  ripening  and  dwarfer  forms.  The  com- 
plete change  of  these  characters  does  not  take  place  in  one  gen- 
eration, but  in  the  course  of  three  or  four  generations  they 
reach  the  limit  of  their  modification.  When  these  grains,  after 
several  years  cultivation  on  the  mountains,  are  again  resown  on 
the  valley  soil,  they  temporarily  ripen  earlier  and  remain  more 
dwarfish  than  their  relatives  that  have  been  continuously  culti- 
vated in  the  valley.  These  characters,  however,  do  not  remain 
permanent,  but  in  a  few  generations  the  plants  go  back  to  their 
former  habits  of  growth. 

Weismann  has  developed  an  elaborate  theory  tending  to  show 
from  a  physiological  standpoint  that  inheritance  of  acquired 
characters  is  impossible.  Every  higher  organism,  both  animals 
and  plants,  is  developed  from  a  single  cell,  the  fertilized  egg. 
Under  circumstances  favorable  for  growth  this  cell  divides  into 
two  equal  portions ;  and  studies  with  the  microscope  have  shown 
that  there  is  a  very  complicated  mechanism  which  makes  this 
division  exact  and  equal.  By  continuous  divisions  of  this  sort, 
the  adult  body  of  every  organism  is  formed.  Some  of  the  cells 
which  are  formed,  however,  are  modified  in  form  and  function, 
and  go  to  make  up  distinct  Organs  and  tissues.  But  there  are 
cells  which  appear  to  have  undergone  no  modification  or  change 
whatever;  these  are  the  reproductive  or  germ  cells  of  the  body. 
If  we  trace  back  to  the  original  germ  cell  from  which  the 
organism  came,  we  see  that  each  cell  of  the  adult  must  have  had 
this  germ  cell  for  a  common  ancestor.  Then  since  the  repro- 
ductive cells  of  this  body  are  qualified  to  transmit  all  of  its 
minute  characters,  it  is  probable  that  they  came  from  the  parent 
egg  cell  by  a  continuous  "careful  division ;  and  have  received  all 
of  its  properties.  The  conclusion  is  that  the  inheritance  of 
qualities  is  transmitted  from  germ  cell  to  germ  cell  in  every  race 
of  organisms  and  that  the  body  is  merely  an  offshoot, — a  house 
built  up  out  of  a  part  of  the  substance  of  the  original  germ  cell 
to  shelter  it  until* it  decays,  and  the  germ  cell  is  transmitted  to 
another  house. 


lO  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    I58. 

It  is  clear  then  that  any  inherited  variation  must  be  a  variation 
which  affects  the  germ  cell,  from  Weismann's  point  of  view ; 
the  use  of  a  particular  organ  of  the  body  would  have  no  effect 
upon  it.  There  is  no  objection,  however,  to  the  belief  that  the 
general  health  of  the  organism  would  affect  the  germ  cells  as 
well  as  any  other  cells  of  the  body.  If  the  environment  is  excel- 
lent for  the  bod)'^  development,  then  the  germ  cell  should  be  well 
nourished  and  able  to  produce  a  healthy  body  in  the  next  genera- 
tion if  it  has  a  fair  chance,  and  vice  versa.  This  theory  would 
readil)^  explain  the  apparent  temporary  inheritance  in  the  case  of 
the  plants  transplanted  from  the  plains  to  the  mountains  and 
back. 

There  are  evidently  certain  characters  which  are  somewhat 
modified  by  environment  and  which  temporarily  transmit  these 
modifications  more  or  less  perfectly;  but  for  a  variation  to-be 
permanently  inherited,  it  seems  probable,  from  both  theory  and 
practice,  that  the  germ  cell  must  he  affected  structurally.  It  is 
unlikely  that  a  temporary  "fattening"  or  "starving"  of  the  germ 
cell  due  to  good  or  poor  nourishment  of  the  body,  is  sufficient 
to  produce  a  permanent  change. 

As  a  possible  inheritance  of  acquired  characters  has  such  a 
broad  bearing  upon  plant-breeding  questions,  we  must  remember 
when  we  come  to  their  discussion,  that  as  yet  such  permanent 
inheritance  is  decidedly  unproved.  Moreover,  such  a  conclusion 
does  not  commit  us  to  a  belief  in  Weismann's  ingenious  but 
unprovable  theories.  The  plant  breeder  only  wishes  to  know 
that  the  relative  probability  of  outside  influences  affecting  the 
structure  of  the  germ  cell  and  thereby  making  new  characters 
heritable — is  extremely  small. 

Darwinism. 
The  great  work  of  Darwin  was  influenced,  if  not  suggested, 
by  an  essay  of  Malthus  on  "Population""  published  in  1798.  Its 
author  gave  incontrovertible '  evidence,  by  data  f  rorn  countries 
all  over  the  world,  that  human  population  tends  to  increase  by 
geometrical  ratio  (that  is,  by  multiplication)  while  food  supply 
tends  to  increase  by  arithmetrical  ratio  (that  is,  by  addition). 
This  means  that  if  human  population  were  ftot  kept  down  by 
disease,  war,  famine  and  other  checks,  the  increase  would  soon 
outrun  the  food  supply.     As  examples  of  similar  but  more  rapid 


EVOLUTION    OF    DARWIN    AND    HIS    PREDECESSORS.  II 

increase  may  be  cited  many  of  the  lower  forms  of  animals, 
which  produce  on  the  average  one  hundred  eggs  and  reproduce 
every  week.  If  the  entire  progeny  of  a  pair  of  such  animals 
were  preserved  living  at  the  end  of  a  year,  their  bulk  zvotild 
exceed  the  limits  of  the  whole  known  universe. 

This  manner  of  increase  is  common  to  a  greater  or  less  degree 
with  all  living  organisms,  both  animals  and  plants;  and  since  space 
and  food  are  not  available  for  such  increase,  it  follows  that  a 
very  large  proportion  of  all  individuals  born  must  perish  without 
producing  offspring.  Darwin's  idea  was  that  out  of  all  the 
individuals  coming  into  existence,  some  will  show  variations  or 
modifications  in  directions  which  adapt  them  better  for  the 
environment  in  which  they  are  placed  than  do  the  characters 
possessed  by  their  less  fortunate  brethren,  and  the  former  will 
survive  at  the  expense  of  the  latter.  This  principle  he  called 
Natural  Selection,  though  later  the  more  common  term  was  that 
of  Herbert  Spencer,  the  "survival  of  the  fittest."  Darwin's  own 
description  of  the  process  is  this : 

"If  under  changing  conditions  of  life,  organic  beings  present 
individual  differences  in  almost  every  part  of  their  structure,  and 
this  cannot  be  disputed;  if  there  be,  owing  to  their  geometrical 
rate  of  increase,  a  severe  struggle  for  life  at  some  age,  season, 
or  year,  and  this  certainly  cannot  be  disputed ;  then,  considering 
the"  infinite  complexity  of  the  relations  of  all  organic  beings  to 
each  other  and  to  their  conditions  of  life,  causing  an  infinite 
diversity  in  structure,  constitution  and  habits — to  be  advanta- 
geous to  them ;  it  would  be  a  most  extraordinary  fact  \i  no 
variations  had  ever  occurred  useful  to  each  being's  welfare,  in  the 
same  manner  as  so  many  variations  have  occurred  useful  to  man. 
But  if  variations  useful  to  any  organic  being  do  occur,  assuredly 
individuals  thus  characterized  will  have  the  best  chance  of  being 
preserved  in  the  struggle  for  life ;  and  from  the  strong  principle 
of  inheritance,  these  will  tend  to  produce  offspring  similarly 
characterized.  This  principle  of  preservation,  or  survival  of  the 
fittest,  I  have  called  Natural  Selection.  It  leads  to  the  improve- 
ment of  each  creature  in  relation  to  its  organic  and  inorganic 
conditions  of  life,  and,  consequently,  in  most  cases,  to  what  must 
be  regarded  as  an  advance  in  organization.  Nevertheless,  low 
and  simple  forms  will  long  endure,  if  well  fitted  for  their  simple 
conditions  of  life." 


12  CONNECTICUT   EXPERIMENT   STATION    BULLETIN    I58. 

The  very  large  amount  of  data  that  Darwin  brought  together 
in  support  of  his  theory,  fell  naturally  under  several  distinct 
heads.  It  was  all  historical  evidence  in  that  it  was  made  up  of  a 
large  number  of  facts  collected  from  the  different  natural  sciences, 
which  were  most  reasonably  explained  by  assuming  evolution  to 
be  true.  It  neither  satisfactorily  explained  how  evolution  took 
place,  that  is,  how  small  a  variation  would  be  preserved  by 
natural  selection,  nor  did  it  show  experimental  evidence  of  the 
actual  production  of  natural  species.  It  is  difficult  to  pick  out 
from  the  mass  of  facts  which  Darwin  had  collected,  particular 
examples  which  are  more  illustrative  than  others,  but  we  will 
endeavor  to  give  particular  cases  from  each  of  the  different  lines. 

Organic  Relationship.  At  the  lower  end  of  both  the  animal 
and  vegetable  kingdom,  we  find  creatures  of  a  very  simple  organi- 
zation. They  are  living  beings  composed  of  one  cell,  and  cannot 
definitely  be  said  to  be  either  animals  or  plants.  Moreover,  these 
organisms  resemble  in  many  ways  the  egg  cell  from  which  all 
higher  animals  and  plants  originate.  From  these  simple  organ- 
isms, we  may  follow  up  the  two  different  and  yet  in  many 
respects  similar  lines  of  organisms  which  go  to  make  up  the 
animal  and  vegetable  kingdoms,  until  we  reach,  on  the  one  hand, 
man,  and  on  the  other,  the  complex  flowering  plants.  The 
gradation  is  noticeable  in  each  line,  although  there  are  many  large 
gaps  which  are.  not  filled  by  any  known  organisms.  The  change 
in  the  simplest  case  is  by  the  addition  of  some  single  character, 
though  in  most  cases  a  number  of  characters  are  different 
between  the  two  nearest  related  kinds  or  species.  First,  there  is 
the  addition  of  more  cells  and  the  single-celled  organism  becomes 
(if  we  may  speak  with  the  definite  idea  of  progress)  a  multi- 
cellular organism.  The  simpler  multicellular  creatures  have  all 
of  their  cells  seemingly  alike.  Then  comes  the  specializing  of 
different  sets  of  cells  to  become  tissues,  and  finally  a  multiplicity 
of  different  tissues  and  organs  useful  for  different  needs  and 
performing  different  functions,  form  the  higher  plants  and 
animals  with  which  we  are  more  familiar. 

Long  before  Darwin's  time,  it  had  been  seen  by  different 
naturalists  that  a  study  of  the  known  animals  and  plants  from 
the  simpler  to  the  most  complex  showed  related  forms.  Some 
were  evidently  very  closely  related,  that  is  they  differed  by  very 
few  essential  characters ;   as  an  eagle  and  a  hawk.     Other  types 


EVOLUTION    OF   DARWIN    AND    HIS    PREDECESSORS.  1 3 

were  very  far  apart,  as  an  oyster  and  a  dog;  and  yet  there  are 
a  number  of  similar  attributes  possessed  by  both  the  oyster  and 
the  dog.  They  both  digest  food,  possess  voluntary  and  involun- 
tary muscles  and  have  circulatory  systems. 

The  natural  result  of  such  study  was  to  show  that  the  plant 
and  animal  kingdoms  could  be  compared  to  a  great  tree,  which 
had  branched  at  the  root  into  two  large  trunks,  each  of  which  is 
divided  into  many  branches.  The  animal  trunk,  for  instance,  has 
one  great  branch  of  fishes  and  another  great  branch  of  birds. 
From  these  great  branches  come  smaller  branches  and  twigs  of 
closer  and  closer  relationship  as  to  characters.  The  whole 
arrangement  seems  to  show  the  development  of  more  complex 
from  less  complex  beings. 

Geographical  Distribution.  In  working  out  this  tree  of  rela- 
tionships, it  has  been  shown  that  groups  of  closely  connected 
creatures  are  often  found  living  in  small  districts,  and  that  when 
a  natural  barrier,  as  an  ocean  or  a  lofty  mountain  range,  is 
passed,  the^-e  is  found  largely  a  new  fauna  and  flora.  Of  course 
there  are  types  of  both  animals  and  plants  that  exist  over  large 
areas,  but  in  most  cases  they  are  species  able  to  migrate  freely 
and  are  adapted  to  the  differences  in  environment  that  have  been 
encountered.  Some  species  live  in  numerous  small  areas:,  the 
mountain  hare,  for  instance,  exists  from  the  Arctic  regions  over 
the  greater  part  of  Europe  in  the  spots  where  there  are  mountain 
ranges  or  climates  cold  enough  to  suit  its  requirements.  It  is  a 
natural  explanation  of  these  facts  to  suppose  that  the  moun- 
tain hare  had  a  continuous  range  over  Europe  during  the 
last  glacial  epoch  when  the  European  climate  was  much  as  the 
present  Arctic  climate.  But  when  the  climate  of  Europe  gradu- 
ally became  temperate,  the  hare  was  able  to  exist  only  on  certain 
mountain  ranges  corresponding  in  climate  to  the  Arctic  regions. 
The  flora  of  the  high  mountain  ranges  also  is  essentially 
Arctic  in  all  of  its  general  characters,  and  yet  the  species  are  not 
the  same  as  those  found  in  the  Arctic  regions.  It  is  not  rational 
to  suppose  that  new  species  were  separately  created  upon  different 
mountain  ranges  after  the  formation  of  the  present  climate  in 
the  temperate  zone,  and  yet  are  so  closely  allied  to  Arctic  species 
as  to  be  included  in  the  same  germs. 

Finally,  it  has  been  shown  that  the  number  of  species  indig- 
enous to  isolated  islands  is  proportional  to  their  biological  isola- 


14  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    I58. 

tion  from  other  larger  or  older  islands.  By  biological  isolation 
is  meant  not  only  distance  in  miles,  but  also  freedom  from  pre- 
vailing winds  or  ocean  currents  from  other  lands.  The  nearer 
islands  are  to  continents,  the  closer  related  are  their  fauna  and 
flora.     As  far  as  is  known  there  is  no  exception  to  this  law. 

Geological  Evidence.  When  Darwin's  theory  was  first  pub- 
lished, there  was  much  criticism  concerning  the  gaps  existing  in 
the  'family  tree'  of  the  animal  and  the  vegetable  kingdom.  Espe- 
cially was  there  a  lack  of  types  possessing  structures  which  would 
show  them  to  be  links  between  the  larger  families  and  orders  of 
animals  and  plants.  It  is  on  this  point  that  modern  study  of 
the  science  of  the  classification  of  animal  and  plant  remains  found 
in  the  dififerent  strata  of  rocks,  which  we  call  paleontology,  has 
produced  such  valuable  evidence.  These  remains  of  ancient  ani- 
mals or  plants  which  we  call  fossils  have  naturally  been  confined 
to  their  hard  parts  such  as  bones  and  teeth,  which  have  been  the 
more  easily  preserved.  However,  from  such  remains  as  were 
available,  large  numbers  of  these  primitive  types  have  been  dis- 
covered and  described.  In  America  has  been  found  a  long  line 
of  remarkable  progenitors  of  the  horse,  leading  back  to  an  animal 
the  size  of  a  dog,  with  four  separate  toes  to  each  fore-leg  and 
three  to  each  hind-leg.  More  striking  still,  in  the  earliest  known 
bird,  the  Archaeopteryx,  the  similarity  to  a  reptile  is  easily  seen. 
The  tail  is  very  long,  with  twenty-one  separate  joints,  every 
joint  bearing  a  feather  upon  each  side.  In  the  modern  bird,  the 
tail  joints  are  very  much  fewer  in  number,  short  and  enlarged, 
and  bear  long  tail  feathers  in  a  fan  shape,  forming  the  so-called 
tail.  This  shortening  up  of  the  tail  did  not  come  at  once  but  is 
seen  in  all  gradations  in  fossil  birds  of  later  periods. 

In  point  of  time  the  geological  evidence  is  found  to  be  exactly 
in  conformation  with  the  theory.  The  earlier  remains  are  those 
of  less  speciaUzed  forms,  while  the  remains  found  in  strata  of 
rocks  of  later  ages  are  of  more  specialized  or  higher  forms.  The 
record  shows  that  of  the  vertebrate  animals,  the  first  to  appear 
were  fishes,  followed  successively  by  amphibians,  reptiles,  birds 
and  mammals.  However,  because  mammals  arose  later  than 
birds,  we  do  not  need  to  conclude  that  mammals  arose  from  birds, 
or  even  from  our  present  form  of  reptiles.  Probably  there  was 
a  diverse  evolution  from  some  early  amphibians  which  gave  rise 
to  reptiles,  birds  and  mammals. 


EVOLUTION    OF   DARWIN    AND    HIS    PREDECESSORS.  1 5 

Geological  evidence  alone  is  not  necessarily  conclusive,  for 
many  fossil  forms  represent  the  highest  development  of  extinct 
types,  and  hence  are  not  progenitors  of  yet  higher  types ;  but 
as  yet  there  are  no  data  among  fossils  that  is  directly  against  the 
theory  of  evolution. 

Comparative  Structures.  The  evidence  of  geology  and  that  of 
classification  is  based  largely  upon  the  study  of  comparative 
structures,  for  the  external  appearance  of  organisms  is  often 
deceiving.  We  must  get  beyond  the  superficial  points  and  study 
,  the  more  permanent  characters.  As  an  example,  the  porpoise 
is  a  fish-like  animal,  its  teeth  being  more  fish-like  than  mammal- 
like; but  on  the  other  hand,  it  suckles  its  young.  Is  it  then  a 
fish  or  a  mammal?  A  mammal  most  assuredly,  for  teeth  are 
very  variable  organs,  while  suckling  the  young  is  characteristic 
of  the  whole  class  of  mammals  and  of  them  alone. 

The  evidence  of  comparative  structures  is  divided  into  two 
parts,  that  of  the  change  of  organs  to  become  better  fitted  for 
different  kinds  of  work,  or  more  useful  under  different  conditions 
of  life,  and  that  of  the  tenacity  with  which  organs  which  are  now 
functionless,  remain. 

Returning  to  the  porpoise  and  its  relative  the  whale,  it  must 
be  inferred  from  the  whole  structure  of  these  animals  that  their 
progenitors  were  terrestrial  quadrupeds  of  some  kind  which  for 
some  reason  became  aquatic  in  their  habits.  Such  a  change  of 
life  made  it  desirable  for  the  animals  to  possess  characters  more 
fish-like.  Probably  such  changes  first  took  place  in  the  most 
variable  parts,  such  as  the  skin,  claws  and  teeth.  Then,  as  time 
went  on,  the  modifications  extended  to  more  typical  structures, 
until  the  whole  shape  of  the  body  was  affected  by  the  bones  and 
muscles  becoming  better  adapted  for  aquatic  than  for  terrestrial 
locomotion.  We  see  in  seals  the  stage  where  the  hind  legs  are 
thrown  backward  until  they  are  of  little  use  on  land,  but  serve  to 
form  a  kind  of  double  fish-like  tail.  In  the  whale  the  modifica- 
tion has  gone  still  further:  the  visible  signs  of  posterior  limbs 
have  entirely  disappeared,  but  there  still  remains  within  the  body 
the  bones  of  a  rudimentary  pelvis  with  indications  of  bones  of  the 
hind  limbs.  The  fore-arm  also,  which  looks  externally  very  like 
a  fin,  still  retains,  in  a  modified  form,  all  of  the  mammalian  bones 
of  the  fore-arm,  wrist  and  hand,  so  that  the  general  appearance  of 
the  skeleton  of  these  parts  bears  a  strong  resemblance  to  that  of 
3 


1 6  CONNECTICUT   EXPERIMENT    STATION    BULLETIN    1 58. 

the  fore-arm  of  man.  Moreover,  the  head,  although  modified 
until  it  resembles  that  of  a  fish,  still  retains  all  of  the  bones  of  the 
mammalian  skull. 

Such  adaptations  to  fit  conditions  of  life  are  very  general  in 
both  animal  and  plant  life.  Plant  adaptations  are  largely  modi- 
fications to  make  sure  of  fertilization  and  consequently  of  very 
definite  use  to  the  species  in  continuing  its  existence.  A  com- 
mon example  noticed  by  everyone  is  the  very  great  amount  of 
pollen  produced  by  maize,  which  is  wind-pollinated,  with  neces- 
sarily a  great  loss.  Compare  this  with  the  small  amount  of 
pollen  produced  by  the  pea,  which  by  its  structure  is  assured 
of  self-polHnation.  Moreover,  there  are  thousands  of  examples 
of  wonderful  modifications*  by  which  plants  secure  animal  aid  in 
their  fertilization, — such  as  showy  blossoms,  secretion  of  nectar, 
and  modified  shapes  of  corollas  which  assure  pollination  by  the 
insects  that  come  to  the  blossoms  for  nectar. 

The  amount  of  evidence  showing  that  once  useful  but  now 
functionless  organs  often  persist  when  their  existence  is  not 
harmful  to  the  organism,  is  not  so  large  as  that  of  which  we 
have  just  been  speaking.  But  certain  vestigial  organs  still 
remain  in  man  which  are  interesting  evidences  of  his  part  in  the 
system  of  evolution,  and  of  his  close  relation  to  the  animals  to 
which  he  feels  superior.  The  tenacious  grasp  of  the  young 
infant  and  the  extreme  natural  inflection  of  the  feet  is  very 
reminiscent  of  the  monkey  family.  The  muscles  of  the  external 
ear  which  are  large  and  of  use  in  quadrupeds,  are  still  retained 
by  man  in  a  small  and  functionless  condition.  The  absence  of 
a  tail  in  man  is  popul|irly  supposed  to  be  a  final  argument  against 
his  quadrumanous  descent.  But  this  is  exactly  what  we  should 
expect,  for  tails  have  been  done  away  with  in  man's  nearest 
relatives,  the  anthropoid  apes.  Man,  however,  as  well  as  the 
apes,  retains  a  few  rudimentary  caudal  vertebrae  at  the  end  of  his 
sacrum  and  even  vestigial  tail  muscles  are  present  in  some 
adults.  Finally  may  be  mentioned  the  vermiform  appendix, 
which  in  its  reduced  size  is  useless  to  man,  and  even  is  harmful 
in  some  cases  as  being  the  seat  of  appendicitis.  In  herbivorous 
animals  the  organ  is  of  large  size  and  functions  in  the  process 
of  digestion.  Some  such  heritages  are  present  in  all  classes  of 
animals  and  plants  and  serve  as  particularly  incontrovertible 
evidence  of  the  relationships  of  different  types. 


EVOLUTION    OF   DARWIN    AND    HIS    PREDECESSORS.  1 7 

Emhryological  Evidence.  Embryology  is  that  branch  of 
biology  that  deals  with  the  formation  and  early  development  of 
organisms.  Such  great  advances  in  the  science  have  been  made 
since  the  time  of  Darwin,  that  many  evolutionists  have  regarded 
it  as  giving  the  principal  evidence  to  the  theory. 

Without  going  into  technical  detail,  the  evolutionary  proofs  of 
embryology  might  be  largely  summed  up  in  the  following  sen- 
tence. The  early  development  of  any  organism  partially  recapit- 
ulates the  embryonic  history  of  its  race  formation.  This  does 
not  mean  that  there  are'  not  many  gaps  in  the  process ;  but  this 
expresses  the  general  tendency  of  development.  As  an  example, 
young  salamanders  before  birth  are  found  to  be  furnished  with 
gills;  and  if  they  are  taken  from  their  mothers  shortly  before 
birth,  the  gills  are  able  to  perform  their  functions,  and  the 
young  salamanders  can  respire  in  water  which  would  drown 
their  own  mothers.  The  complete  formation  of  gills  in  the 
embryo  salamander  is  an  entire  waste  of  time,  as  the  gills  are 
never  of  use  in  the  normally  developed  young.  It  is  clear,  then, 
that  one  could  only  expect  such  a  phenomenon  to  happen  from 
the  viewpoint  of  a  previous  evolution. 

In  man  himself  there  are  stages  in  the  development  of  the 
embryo  when  it  is  scarcely  distinguishable  from  the  embryos 
of  any  of  the  other  vertebrates,  such  as  fish,  amphibians,  rep- 
tiles, birds  or  lower  animals.  It  early  possesses  the  two-cham- 
bered heart  of  the  fish,  and  gill  slits  of  undeveloped  gills. 
Further  on  in  its  development,  the  embryonic  heart  has  the  three 
chambers  characteristic  of  amphibians  and  finally  the  four- 
chambered  heart  characteristic  of  the  double  circulation  of  birds 
and  mammals. 

Variation  under  Domestication.  In  the  study  of  the  varied 
forms  of  our  domestic  animals  and  cultivated  plants,  Darwin 
found  a  great  deal  of  his  best  data  regarding  the  variability  of 
organisms.  He  showed  that  particularly  among  domestic 
animals,  for  example  the  pigeons,  there  are  varieties  descended 
from  a  common  wild  ancestor,  which  if  met  with  in  a  state  of 
nature  would  be  classed  as  different  species  and  possibly  as 
different  genera.  There  is  no  reason  to  believe  that  animals  in 
the  wild  state  are  not  just  as  variable  as  domestic  animals, 
although  man  undoubtedly  selects  and  perpetuates  variations 
which  would  not  be  of  sufficient  value  to  the  organism  to  survive 


1 8  CONNECTICUT   EXPERIMENT    STATION    BULLETIN    1 58. 

by  natural  selection.  However,  proof  of  such  variation  of 
characters  of  specific  rank  is  proof  enough  that  sometimes  there 
must  occur  variations  which  are  sufficiently  useful  to  protect  their 
possessors  in  the  struggle  for  existence  that  we  saw  is  con- 
tinually taking  place  in  nature. 

Such  in  brief  were  the  lines  of  argument  brought  together  by 
Darwin  in  support  of  his  evolution  theory;  and  with  such  bril- 
liancy and  with  so  man}^  data  did  he  maintain  it  that  before  his 
death  practically  the  whole  thinking  world  was  converted  from 
the  orthodox  Jewish  belief  in  the  special  creation  of  every 
species,  to  that  of  the  development  of  all  organisms  from  very 
primitive  types. 

To  summarize  the  whole  question,  we  may  state  just  what 
were  the  fundamental  points  which  Darwin  proved.  The  over- 
whelming amount  of  his  historical  data,  as  we  have  seen,  left 
no  reason  to  doubt  that  there  had  been  an  organic  evolution. 
In  order  for  a  natural  organic  evolution  to  have  taken  place  there 
must  have  been  three  cooperative  factors :  first,  variability  within 
species ;  second,  a  capacity  among  organisms  for  transmitting 
particular  characters ;  and  third,  a  means  of  selection  of  varia- 
tions for  perpetuation. 

Many  examples  of  sufficient  variability  were  easily  found 
among  existing  data,  though  it  is  true  they  were  generally  con- 
fined to  domestic  animals  and  plants ;  and  there  was  no  reason  to 
doubt  that  certain  variations  of  sufficient  specific  character  had 
been  inherited  under  man's  selection.  As  to  his  natural  selec- 
tion factor,  it  was  unquestionably  shown  that  there  was  and  is  a 
struggle  for  existence  in  which  the  greater  part  of  all  organisms 
coming  into  being,  perish.  Variations  sufficiently  of  advantage  to 
their  possessors,  to  make  their  attaining  adult  life  and  reproduc- 
ing their  kind  relatively  more  probable,  would  obviously  survive. 
These  facts  will  stand  forever  as  a  sufficient  monument  to  the 
memory  of  Darwin. 

The  questions  to  which  he  did  not  give  a  sufficient  answer  are : 
first.  What  is  the  physiological  meaning  of  the  different  kinds  of 
variation?  second,  how  great  must  a  variation  be  to  be  selected, 
or  how  often  must  it  occur  to  have  stability?  third,  what  is  the 
rate  of  inheritance  of  different  kinds  of  variation?  fourth,  what 
is  the  mechanism  of  inheritance?    and  fifth,  must  only  favorable 


EVOLUTION    OF   DARWIN    AND    HIS    PREDECESSORS.  1 9 

variations  be  selected  or  will  variations  which  are  simply  non- 
injurious  survive?  In  other  words,  Darwin  proved  the  fact  of 
evolution  and  established  one  of  its  great  working  principles,  but 
left  to  the  future  to  largely  explain  its  detailed  mechanism. 

The  criticisms  of  Darwin's  work  are  many  and  a  large  number 
of  them  are  very  just,  but  they  do  not  affect  the  truth  of  general 
Organic  Evolution.  Huxley  well  expressed  the  facts  when  he 
said:  "Even  if  the  Darwinian  hypothesis  were  swept  away, 
evolution  would  still  stand  where  it  is."  The  criticisms  that  are 
at  all  pertinent  concern  the  five  questions  just  given.  Other 
criticisms  are  largely  due  to  a  misunderstanding  of  Darwin's 
own  work.  His  work  was  so  broad  that  he  himself  fairly 
stated  a  large  number  of  the  criticisms  that  were  brought  to  bear 
upon  it.  He  recognized  that  the  detail  of  the  manner  in  which 
evolution  took  place  was  yet  almost  untouched  by  investigation. 
Yet  in  many  of  these  issues  the  problems  were  outlined  by  the 
hand  of  a  master. 

It  is  odd,  at  first  thought,  that  all  of  the  important  criticisms 
are  of  primary  and  direct  importance  to  plant  breeding;  yet  it 
really  is  not  odd,  for  the  factors  in  the  improvement  of  crops 
are  the  same  as  those  of  a  natural  evolution.  There  are  the  same  ^ 
classes  of  variations  to  deal  with,  the  same  questions  of  inherit- 
ance of  these  variations.  It  is  true  that  artificial  selection  takes 
the  place  of  natural  selection,  but  also  here  it  is  imf)ortant  to  know 
in  each  case  whether  the  laws  of  inheritance  are  such  that  a 
single  useful  variation  which  has  occurred,  can  be  preserved,  or 
if  it  must  be  lost  by  intercrossing  with  individuals  not  possessing 
the  variation. 

In  the  next  chapter,  we  deal  with  some  of  the  points  of  evolu- 
tionary criticism  which  have  affected  our  entire  conception  of 
the  methods  to  be  used  in  plant  breeding. 


20  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    1 58. 

II. 

Later  Evolutionary  Theories  and  Principles. 
Criticisms  of  Darwin's  Mechanical  Theory. 

There  are  two  main  classes  of  variations,  both  of  which  Darwin 
recognized  as  agents  in  the  work  of  evolution.  The  first  he 
called  "fortuitous"  or  chance  variations,  although  he  admits  that 
this  is  an  incorrect  expression  which  serves  only  to  plainly 
acknowledge  our  ignorance  of  the  exact  cause  or  causes  of  each 
particular  variation.  This  is  the  common  type  of  variation  seen 
in  every  growing  plant  and  animal.  It  is  now  called  fluctuating 
variation,  and  each  individual  variation  a  fluctuation, — terms 
which  we  shall  henceforth  use.  Illustrations  of  fluctuating  varia- 
tion are  found  in  every  character  of  all  living  organisms ;  which 
is  the  same  as  saying  that  no  two  plants  or  animals  are  exactly 
alike.  Take  as  an  example  a  number  of  ears  of  maize.  They 
may  be  of  the  same  variety,  have  grown  on  the  same  soil,  and 
have  had  exactly  the  same  treatment  during  the  growing  season ; 
nevertheless  they  differ  among  themselves  in  length,  in  circum- 
ference, in  weight,  in  number  of  rows,  in  fact  in  every  character 
we  may  pick  out. 

The  second  class  of  variations  are  those  which  Darwin  called 
"definite"  or  discontinuous  variations.  To  this  kind  of  variation 
belong  those  characters  that  suddenly  appear  in  their  perfection, 
capable  of  transmitting  the  new  feature  with  only  the  ordinary 
amount  of  fluctuating  variation.  These  variations  are  now 
called  mutations.  To  illustrate  our  meaning  take  the  peach  tree. 
It  is  not  an  uncommon  thing  for  one  branch  to  bear  those  smooth- 
skinned  fruits  called  nectarines.  This  is  mutation,*  which  con- 
tinues constant  from  year  to  year.  The  nectarines,  however, 
differ  among  themselves  in  size,  weight,  amount  of  flesh  and 
other  characters.  In  other  words,  they  still  have  fluctuating 
variations  among  themselves.  Galton  illustrates  the  point  of 
distinction  nicely  by  use  of  a  polyhedron, — an  object  with  a  num- 
ber of  equal  sides.     Suppose  some  force  rocks  the  polyhedron  as 


*  Some  writers  refuse  to  recognize  bud  mutations  as  real  mutations,  but 
as  bud  mutations  are  sometimes  transmitted  by  seed,  there  seems  to  be  no 
reason  for  their  exclusion  until  a  definite  scientific  distinction  between 
them  and  germ  mutations  is  known. 


LATER   EVOLUTIONARY   THEORIES    AND    PRINCIPLES.  21 

it  rests  upon  one  of  its  faces.  It  will  rock  back  and  forth  but 
always  tends  to  come  to  rest  upon  this  face.  These  oscillations 
represent  fluctuating  variation.  But  should  a  sudden  shock  rock 
the  object  so  violently  that  it  finally  comes  to  rest  on  another  of 
its  faces,  we  might  think  of  it  as  a  mutation.* 

Darwin  believed  that  evolution  and  the  changes  in  domestic 
animals  and  plants  were  very  largely  the  result  of  the  selection 
of  the  small  individual  variations  or  fluctuations,  as  the  following 
quotation  shows : — 

"It  may  be  doubted  whether  sudden  and  considerable  devia- 
tions of  structure  such  as  we  occasionally  see  in  our  domestic 
productions,  more  especially  with  plants,  are  ever  permanently 
propagated  in  a  state  of  nature.  Almost  every  part  of  every 
organic  being  is  so  beautifully  related  to  its  complex  conditions 
of  life  that  it  seems  as  improbable  that  any  part  should  have  been 
suddenly  produced  perfect,  as  that  a  complex  machine  should 
have  been  invented  by  man  in  a  perfect  state.  ...  If  mon- 
strous forms  of  this  kind  ever  do  appear  in  a  state  of  nature 
[he  was  speaking  of  a  pig  which  had  been  born  with  a  short  pro- 
boscis, E.  M.  E.]  and  are  capable  of  reproduction  (which  is  not 
always  the  case),  as  they  occur  rarely  and  singly,  their  preserva- 
tion would  depend  on  unusually  favorable  circumstances.  They 
would,  also,  during  the  first  and  succeeding  generations,  cross 
with  the  ordinary  form,  and  thus  their  abnormal  character  would 
almost  inevitably  be  lost." 

It  is  only  fair  to  say  that  Darwin  changed  his  views  slightly 
in  the  last  edition  of  his  work.  So  many  examples  of,  mutations 
had  come  under  his  notice  that  he  could  not  disregard  them 
entirely,  and  he  says :  "In  the  earlier  editions  of  this  worl?  I 
underrated,  as  it  now  seems  probable,  the  frequency  and  impor- 
tance of  modifications  due  to  spontaneous  [mutations]  variability. 
But  it  is  impossible  to  attribute  to  this  cause  the  innumerable 
structures  which  are  so  well  adapted  to  the  habits  of  life  of  each 
species." 

We  shall  see  later  from  the  work  of  De  Vries  that  mutations 
do  not  necessarily  occur  singly,  and  from  the  work  of  Mendel,, 
that  they  would  not  need  to  be  swamped  by  intercrossing;    but 

*  De  Vries  believes  fluctuations  are  confined  to  plus  or  minus  variations 
of  the  same  character;  that  is,  "linear"  variations.  Mutations,  on  the 
other  hand,  may  take  place  in  any  direction. 


2  2  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    1 58. 

we  will  now  take  up  some  of  the  earlier  criticisms  of  Darwin's 
views  that  are  particularly  related  to  the  part  played  by  fluctua- 
tions and  mutations  in  evolution, 

A  great  obstacle  toward  explaining-  all  adaptive  structures  by 
the  use  of  natural  selection  is  the  fact  that  many  structures 
which  are  useful  in  a  fully  developed  state  must  have  been  use- 
less in  the  beginning  when  rudimentary  and  undeveloped.  This 
criticism  has  been  made  by  all  opponents  of  the  theory,  but  was 
stated  with  particular  force  by  the  Duke  of  Argyll.  He  argues 
that  if  an  organ .  was  developed  gradually  and  very  slowly,  it 
follows  as  a  matter  of  course  that  every  beginning  of  such  an 
organ  must  have  been  functionless  at  first.  "No  structure  can 
be  selected  by  utility  in  the  struggle  for  existence  until  it  has 
not  only  been  produced,  but  has  been  so  far  perfected  as  to 
actually  be  used."  For  example,  the  eye  of  animals  or  the  wing 
of  birds,  he  thinks,  could  not  have  been  of  sufficient  use  to  the 
possessors  of  their  first  rudiments  to  have  caused  them  to  have 
been  selected.  Romanes,  in  replying  to  this  criticism,  thinks  that 
even  if  only  rudimentary  as  eye  or  wing,  they  may  have  been 
useful  for  other  purposes.  A  nerve  ending  may  have  been  sensi- 
tive in  a  slight  degree  to  light,  and  thus  have  enabled  the  animal 
to  find  more  food  or  to  hide  itself  better  from  its  enemies.  Like- 
wise a  rudimentary  wing  might  not  have  been  useful  for  flight 
but  still  have  served  for  more  rapid  locomotion.  These  explana- 
tions, while  ingenious,  seem  to  be  rather  strained  and  make  us 
feel  as  if  we  should  rather  have  some  theory  which  does  not  put 
too  great  a  burden  on  our  faith. 

Morgan  has  put  forth  an  objection  belonging  to  this  same  class 
which  is  even  more  pertinent.  Many  species  of  animals  have 
the  power  to  regenerate,  or  grow  again,  certain  parts  of  the  body, 
when  lost  by  accident.  It  is  absurd  to  think  of  natural  selection 
as  preserving  an  individual  which  has  this  power  in  a  very  slight 
and  imperfect  manner,  and  by  a  continued  selection  of  those 
individuals  that  can  better  regenerate  lost  parts, — finally  perfect- 
ing this  power.  It  has  been  shown  experimentally  that  only  a 
small  per  cent,  of  the  animals  of  a  species  possessing  this  power 
ever  lose  a  limb  or  other  part.  What  chance  would  they  have  of 
surviving  by  natural  selection  in  competition  with  numerous 
perfect,  healthy  specimens?  The  only  possible  explanation  of 
the  perfecting  of  such  a  power  by  the  selection  of  small  fluctuat- 


LATER    EVOLUTIONARY    THEORIES    AND    PRINCIPLES.  23 

ing  variations  is  that  they  might  be  dependent  upon  other  varia- 
tions in  structure  which  were  useful  when  rudimentary.  We 
know  that  sometimes  seemingly  independent  structures  do  go 
together  in  an  unaccountable  manner,  a  phenomenon  which  is 
called  correlated  variation.  But  here  again,  such  an  explana- 
tion is  as  unsatisfactory  support  as  is  a  straw  to  a  drowning  man. 

There  are  at  least  four  important  objections  among  early 
criticism  which  cannot  admit  explanation  by  the  natural  selection 
theory  alone : — first,  that  a  large  proportion  of  the  characters  that 
distinguish  species  from  each  other  are  seemingly  useless  and 
therefore  cannot  be  explained  by  a  use  selection;  second,  the 
most  common  of  specific  characters,  sterility  between  species, 
Darwin  himself  showed  could  not  be  explained  by  natural 
selection ;  third,  the  swamping  effects  of  free  intercrossing  would 
render  impossible  by  natural  selection  any  evolution  of  species  in 
divergent  lines  ;*  fourth,  many  characters  useless  for  the  preserva- 
tion of  individuals  have  been  developed  by  only  one  sex  of  a  given 
species.  In  the  latter  class  belong  the  beautiful  plumage 
developed  by  many  male  birds.  Darwin  has  developed  a  theory 
supplementary  to  natural  selection,  that  he  calls  sexual  selection, 
to  account  for  such  cases.  In  brief,  it  is  that  higher  animals  do 
not  mate  at  random  but  exercise  an  instinctive  choice  in  obtaining 
their  nuptial  partners.  The  female  cardinal  or  redbird,  for 
example,  has  had  an  instinctive  liking  for  a  scarlet  color.  In  the 
early  history  of  the  species,  males  were  accepted  as  mates  by  the 
females  only  when  they  possessed  certain  red  markings  that  had 
appeared  as  variations  upon  the  plumage  of  certain  individuals. 
These  particular  males  were  sires  of  the  greater  part  of  the  next 
generation,  and  thus  impressed  upon  it  a  large  amount  of  their 
characteristics.  A  continuation  of  this  process  is  thought  to  have 
produced  the  characteristic  coat  of  the  male  of  the  species.  Why 
only  the  males  of  some  species  possess  certain  characters  to  the 
exclusion  of  the  females,  our  present  knowledge  of  heredity 
ofifers  no  explanation.  Sexual  selection  seems  a  reasonable 
explanation  for  the  evolution  of  a  few  characters  belonging  to  this 
class,  but  it,  like  natural  selection,  has  been  given  more  and 
broader  phenomena  to  explain  than  it  can  possibly  cover. 

These   earlier   criticisms   conclusively  show   that   the   natural 
selection  theory  is  mainly,  as  Morgan  states,  a  theory  of  adaptation 


*See  Mendel's  work  for  an  explanation  of  this  objection. 
.4 


24  CONNECTICUT    EXPERIMENT   STATION    BULLETIN    I58. 

to  environment.  It  is  a  sieve  which  sifts  out  variations  which 
have  appeared  that  are  of  prime  utility  to  the  organism  or  to  the 
species.  It  is  not  a  cause  of  evokition  itself,  but  a  working 
agent  for  destroying  organisms  less  fit  for  their  station  in  life  than 
some  of  their  relatives  or  species  less  fit  for  existence  than  others. 
It  is  not  a  selective  agency,  but  a  rejective  agency.  It  is  plainly 
evident  that  it  is  one  of  the  great  factors  of  evolution,  possibly 
the  greatest  factor;  but  it  is  as  plainly  evident,  even  with  the 
added  theory  of  sexual  selection,  that  numerous  characters  pos- 
sessed by  living  organisms  must  have  developed  without  its 
agency. 

We  will  next  mention  the  more  recent  criticisms  of  Darwin's 
theory,  which  have  to  do  with  the  probability  of  evolution  having 
taken  place  through  the  selection  of  fluctuating  variations.  Lord 
Kelvin  has  furnished  the  first  telling  obstacle  by  his  calculations 
of  the  age  of  the  earth.  Earlier  geologists  and  biologists,  when 
they  had  once  turned  away  from  the  idea  that  the  earth  was  only 
about  six  thousand  years  old,  allowed  themselves  to  suggest 
millions  of  millions  of  years  as  the  amount  of  time  necessary  for 
the  geological  changes  and  those  of  evolution  to  have  taken  place. 
These  ideas  in  turn  were  forced  to  give  way  when  Lord  Kelvin 
calculated  the  earth's  age  upon  definite  physical  data.  His  cal- 
culations were  divided  into  three  sets :  first,  based  upon  the  rate 
of  the  earth's  rotation  as  affected  by  the  retardation  of  the  tides ; 
second,  based  upon  the  rate  of  cooling  of  the  earth,  calculated 
from  the  rate  at  which  the  temperature  increases  on  boring 
inward  toward  its  centre ;  third,  based  upon  the  rate  of  cooling  of 
the  sun  by  radiation.  There  was  a  noteworthy  agreement  in 
these  three  calculations,  all  tending  to  show  that  less  than  one 
hundred  million  years  has  elapsed  since  the  earth's  surface  has 
been  in  a  condition  to  support  life.  These  calculations  have  been 
somewhat  changed  since  the  discovery  of  the  immense  amount  of 
energy  stored  up  in  radioactive  substances,  yet  it  still  remains 
necessary  to  conclude  that  life  has  not  flourished  on  this  planet 
a  sufficient  length  of  time  to  have  developed  our  present  fauna 
and  flora  solely  by  the  selection  of  fluctuating  variations. 

De  Vries  has  attacked  the  question  of  the  probability  of  evolu- 
tion through  the  selection  of  fluctuations  from  another  point,  that 
of  their  inheritance.  He  believes  that  fluctuations  are  a  kind  of 
acquired  characters;    at  least  that  they  depend  solely  upon  the 


LATER   EVOLUTIONARY   THEORIES    AND   PRINCIPLES.  25 

effect  of  food,  light,  temperature,  moisture  and  other  factors  of 
environment.      Nevertheless,    they    are,    in    a    certain    degree, 
inherited.     There  is  nothing  unusual  in  this  when  we  consider 
that  all  higher  organisms  are  but  collections  of  cells  each  with  its 
own  purpose  to  fulfill.     Should  the  environment  of  an  individual 
be  particularly  favorable  so  that  its  general  health  is  above  the 
average,  then  might  not  the  reproductive  cells  be  better  nourished 
and  they  therefore  be  enabled  to  produce  better  organisms,  owing 
to  their  better  start  in  life?     We  should  expect,  however,  that 
such  improvement  would  not  be  permanent,  but  would  cease  if  the 
selection  of  such  individuals  was  abandoned,  and  even  degenerate 
to  the  original  type.     This  is  exactly  what  has  been  found  both  in 
historical  cases  and  in  experiments.     The  improvement  of  sugar 
beets  in  their  sugar  content  has  now  been  in  progress  for  about 
fifty  years,  yet  the  maximum  improvement  was  obtained  in  a 
very  few  years  after  the  start,  and  now  all  that  continued  selec- 
tion of  the  highest  fluctuations  of  sugar  content  can  do  is  to  keep 
the  average  up  to  the  point  to  which  it  had  been  raised  years  ago. 
As  an  experiment  upon  this  point,  De  Vries  tried  to  raise  the 
average  number  of  rows  of  a  variety  of  maize  by  selection.     This 
variety  had  an  average  of  13  rows  per  ear.     As  we  know,  no 
ears  of  maize  have  an  odd  number  of  rows,  but  the  average  was 
between  12  and  14  rows  per  ear;     The  actual  number  of  rows  in 
individual  cases  varied  between  8  and  22.     He  planted  an  ear 
having  16  rows  and  in  the  crop  found  a  new  average  of  15  rows 
per  ear.     From  this  crop  some  good  ears  bearing  20  rows  were 
planted,  and  this  process  of  selection  was  continued  annually  for 
six  seasons.     At  the  end  of  this  time  the  average  of  the  variety 
had  reached  20  rows.     The  lowest  number  on  any  ear  was  then 
12  and  the  highest  found  was  28,  a  number  which  he  had  never 
seen  in  the  regular  variety.     There  are  two  points  to  be  con- 
sidered in  this  experiment,  as  De  Vries  points  out.     The  first  is : 
Could  this  average  of  20  rows  have  been  obtained  in  one  year? 
On  examining  the  results  of  the  different  years  it  was  found  that 
an   average  increase   was  obtained  equal  to   two-fifths  of  the 
deviation  of  the  parent  ear  from  the  average.     An  average  of 
20   rows   per   ear   is   a    deviation   of    7    from   the   average   of 
the  original  variety  of  13  rows  per  ear.     Then  if  7  equal  two- 
fifths  of  the  deviation,  to  obtain  an  average  deviation  of  7  in  the 
progeny,  we  should  need  a  deviation  of  17^   rows  above  the 


26  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    I58. 

average  13  rows;  that  is,  a  selected  ear  containing  30-32  rows. 
Two  hundred  ears  had  been  examined  originally  and  one  22- 
rowed  ear  was  found.  Now  by  the  mathematics  of  probability, 
we  can  predict  that  by  doubling  the  number  of  ears  examined 
we  would  expect  to  find  one  ear  with  one  more  row,  or  23  rows. 
This  means  that  by  the  examination  of  100,000*  ears,  he  would 
have  had  the  same  likelihood  of  finding  an  ear  of  32  rows  as  he 
had  of  finding  the  ear  of  22  rows  when  he  examined  the  two 
hundred. 

The  point  is  this:  By  examining  100,000  ears  he  could  prob- 
ably have  found  and  planted  an  ear  containing  32  rows  and 
would  have  obtained  his  race  of  corn  averaging  20  rows  to  the 
ear  in  one  season.  But  by  taking  six  years  for  the  selection, 
he  was  able  to  obtain  the  20-rowed  race  by  the  use  of  only 
about  1,000  plants.  Hence  the  gradual  change  that  takes  place 
in  the  t3^pe  of  a  selected  fluctuating  character  is  apparent  rather 
than  real,  and  is  due  to  the  rejection  and  non-propagation 
during  the  breeding  of  so  many  numbers  below  the  selection 
standard. 

The  second  important  point  is :  Does  an  average,  such  as 
De  Vries  obtained  for  his  corn  after  six  years  selection,  remain 
constant  ?  To  test  this  point  De  Vries  allowed  the  20-rowed 
race  to  propagate  indiscriminately  and  found  that  in  only  three 
or  four  years  the  old  type  of  13-rowed  corn  was  reached. 
A  number  of  other  instances  could  be  cited  that  indicate  that  all 
races  improved  by  the  selection  of  fluctuating  variations  are 
inconstant  and  tend  to  return  to  their  original  type.  This  con- 
clusion is  perfectly  in  accord  with  the  conclusion  we  reached  in 
the  last  chapter  regarding  acquired  characters. 

These  conclusions  of  De  Vries  regarding  the  inconstancy  of 
races  improved  by  selection  of  fluctuations,  have  in  the  main  been 
confirmed  by  an  entirely  different  school  of  investigators  called 
biometricians.  Biometry  is  the  science  of  applying  mathematical 
methods  of  dealing  with  statistics  to  biological  problems.  It  is 
not  necessary  for  us  to  go  into  their  technical  methods,  but  we 
must  give  two  of  their  important  discoveries,  whose  derivation 
it  is  not  necessary  to  understand  to  appreciate  their  value. 


*  There  is  necessarily  a  physical  limit  in  the  production  of  rows  in  ears 
of  maize,  as  in  all  other  natural  productions.  Above  this  limit  mathe- 
matical calculation  is  valueless. 


LATER    EVOLUTIONARY   THEORIES    AND    PRINCIPLES. 


27 


The  first  is  called  Quetelet's  law.  Quetelet,  a  Belgian  astrono- 
mer about  the  middle  of  the  last  century,  discovered  that  the 
relative  frequency  of  the  occurrence  of  fluctuating  variations  in 
living  organisms  obeys  the  mathematical  theory  of  probability; 
that  is,  it  is  just  what  we  should  expect  if  the  number  of 
causes  combining  to  make  fluctuations  in  nature  is  infinitely 
large.  For  example,  we  measured  the  lengths  of  a  hundred  and 
eighty-six  ears  of  a  certain  variety  of  corn  and  found  that  they 
fell  into  classes  of  one  inch  in  the  following  manner. 


Length  in  inches 
Frequenc)'^   


314 
o|i 


6  1    7  I    8  1    g  I  10  I  n  I  12  I  13  I  14 
5  I  19  I  37  I  58  I  40  I  18  I    6  I    I  I    o 


Now  if  we  draw  a  horizontal  line  and  divide  it  into  equal  parts 
marked  with  these  classes  of  one  inch  each ;  then  erect  per- 
pendiculars at  each  point  proportional  in  height  to  the  number  of 


4  5  6  7  8  9  10  "  It  13 

Fig.  I.     Frequency  polygon  or  curve  of  variation  in  length  of  maize  ears 


ears  found  in  each  class;  by  joining  the  tops  of  these  perpen- 
diculars we  get  a  close  approximation  to  what  the  mathema- 
ticians call  the  normal  curve.  By  knowing  this  fact,  we  can 
predict  approximately  how  many  ears  of  a  certain  length  we 
should  find  in  one  thousand  ears  of  this  variety. 

The  second  great  law  of  the  biometricians  is  called  the  law 
of  ancestral  heredity.  It  was  enunciated  by  Galton  but  received 
modification  and  confirmatory  data  from  Pearson.  In  its  present 
form,  it  supposes  that  the  average  resemblance  of  this  offspring 
to    the    two    parents    is    50    per    cent.,    to    the    four    grand- 


2  8  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    1 58. 

parents  25  per  cent.,  and  to  the  eight  great-grandparents   12.5 
per  cent,  and  so  on.* 

Assuming  the  truth  of  the  law  of  ancestral  heredity,  and  a 
perfectly  normal  distribution  of  fluctuations,  Pearson  has  shown 
what  could  be  accomplished  by  continued  selection,  provided  all 
biological  data  followed  the  laws  that  he  has  found  in  his  data 
from  measurements  of  the  human  race.  The  conclusions  were 
derived  from  measurements  of  several  different  characters,  but 
the  following  will  serve  as  an  imaginary  example  to  illustrate  his 
results.  If  the  average  height  of  the  population  were  five  feet 
and  six  inches,  and  individuals  six  feet  high  were  selected  as 
parents,  then  in  the  first  generation  he  has  found  that  the  average 


M 

Fig.  2.     Normal  curve 

Compare  with  Fig.  i. 

height  of  the  offspring  would  be  five  feet  six  inches  plus  62  per 
cent,  of  six  inches,  which  is  the  deviation  of  the  parents  from 
the  average.  Again  selecting  six-foot  parents,  the  height  of  the 
offspring  would  be  five  feet  six  inches  plus  82  per  cent,  of  six 
inches,  and  in  the  third  generation  five  feet  six  inches  plus  89 
per  cent,  of  six  inches.  Selection  of  six-foot  parents  for  a  large 
number  of  generations  would  only  bring  the  average  up  to  five 
feet  six  inches  plus  92  per  cent  of  six  inches.     This  shoyvs  that 


*  This  law  has  been  much  misunderstood,  and  a  great  deal  of  criticism 
of  it  has  arisen  through  the  activities  of  the  Mendelian  school  of  biologists. 
If  we  consider  a  single  character  possessed  by  the  organism,  it  may  be 
generally  untrue,  but  if  we  consider  all  of  the  thousands  of  characters 
possessed  by  the  organism,  it  certainly  approximates  the  truth. 


LATER    EVOLUTIONARY   THEORIES    AND    PRINCIPLES.  29 

in  three  or  four  generations  the  offspring  may  have  an  average 
of  90  per  cent,  of  the  selected  character,  but  after  this  selection 
has  only  little  effect.  Moreover,  Pearson  showed  that  if  selec- 
tion was  stopped  at  any  time  and  the  offspring  allowed  to  inbreed, 
they  quickly  returned  toward  the  average  of  the  selected  character 
in  the  original  race. 

Recently  some  tentative  conclusions  of  Johannsen's,  from 
experiments  upon  barley  and  kidney  beans,  may  be  interpreted 
as  agreeing  with  Weismann's  theory,  and  De  Vries'  and  Pear- 
son's conclusions, — that  fluctuating  characters  have  almost  noth- 
ing to  do  in  the  permanent  improvement  of  a  race.  All  of  his 
experiments  were  made  upon  plants  which  could  be  self- fertilized 
during  successive  generations.  In  this  way  he  made  the  experi- 
ment simpler  than  he  could  have  done  if  he  had  used  different 
plants  for  the  two  parents.  All  of  the  descendants  of  a  single 
plant,  arising  by  self-fertilization,  he  speaks  of  as  a  'pure  line.' 
The  characters  used  were  typical  fluctuating  characters  such  as 
the  weight  of  the  seeds.  All  members  of  a  pure  line  showed 
normal  fluctuations  around  a  mean  or  type  value.  Moreover,  all 
seeds  from  plants  of  the  same  variety,  made  up  of  a  number  of 
such  pure  lines,  also  showed  a  normal  variability.  In  the  pure 
lines,  some  of  the  mean  or  type  values  were  very  close  to  the 
mean  of  the  variety  in  general,  while  others  were  quite  different, 
being  both  lower  and  higher  than  the  general  mean  value.  When 
any  individual,  differing  widely  from  the  mean  value  of  its  pure 
line,  was  selected  for  propagation,  its  offspring  showed  a  regres- 
sion or  tendency  to  go  back  toward  the  type  of  its  particular  line; 
but  showed  no  regression  to  the  mean  value  of  the  variety. 

It  is  quite  clear  if  these  conclusions  are  warranted,  that  the  only 
improvement  that  selection  can  effect  is  towards  the  isolation 
of  one  of  these  pure  lines  and  must  of  a  necessity  come  to  an 
end  when  the  pure  line  is  entirely  isolated.  The  difficulty  of 
doing  this  in  practical  work  is  obviously  very  great  because  of 
natural  intercrossing.  It  was  the  opinion  of  Darwin  that  by 
selection  the  type  of  the  race  would  be  raised  and  a  new  selection 
possible  from  the  extremes  in  fluctuation  of  this  new  type.  This 
would  set  no  limit  to  the  amount  of  improvement  that  could  b§ 
made.  The  experiments  of  De  Vries  and  Pearson,  however,  and 
the  experience  of  breeders  in  general  as  illustrated  by  the  case  of 
the  sugar  beet  seem  to  agree  with  Johannsen's  theory,  that  such 


30  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    I58. 

is  not  the  case.  Johannsen's  work,  however,  indicates  that  the 
complete  isolation  of  a  pure  line  would  give  a  strain  which  would 
not  regress  to  the  mean  of  the  original  mixed  population,  but 
would  breed  true  to  its  own  type.  This  is  contrary  to  the  general 
belief  of  breeders,  and  his  further  results  will  be  awaited  with 
great  interest; 

The  results  of  our  considerations  of  the  criticism  of  Darwin's 
theory,  that  evolution  must  take  place  through  natural  selection 
or  some  kindred  eliminating  agency  as  sexual  selection  of  minute 
fluctuating  variations,  have  led  to  three  general  conclusions^^ 
First,  natural  selection  will  not  explain  either  the  evolving  of 
many  characters  that  could  not  have  been  useful  in  a  rudimentary 
state,  or  the  large  numbers  of  characters  that  appear  to  be  entirely 
useless  to  organisms.  Second,  the  age  of  the  earth  since  the 
formation  of  oceans,  as  calculated  by  physicists,  does  not  allow 
sufficient  time  for  the  evolution  of  higher  plants  and  animals  by 
the  selection  of  minute  fluctuating  variations.  Third,  experi- 
mental evidence  from  several  diverse  lines  all  tends  to  show  that 
a  selection  of  fluctuating  variations  can  make  no  permanent 
improvement,  and  that  there  is  a  narrow  limit  to  the  changes  that 
can  be  made,  even  with' their  continuous  selection. 

The  Mutation  Theory. 

The  study  of  evidence  relating  to  the  points  that  have  just 
been  discussed,  has  resulted  in  a  waning  belief  in  the  efficiency 
of  fluctuating  variations  to  explain  the  facts  of  evolution, 
and  in  a  growing  belief  in  the  prominent  part  played  by 
discontinuous  variations  or  mutations.  We  owe  to  Hugo  De  Vries, 
an  eminent  Dutch  botanist,  the  largest  amount  of  data  regard- 
ing mutations,  and  even  the  word  itself  when  used  in  this  sense. 
It  is  true,  other  prominent  workers  were  beginning  to  trace  out 
similar  theories,  and  particularly  important  experiments  had  been 
conducted  by  the  distinguished  English  zoologist,  Bateson ;  but 
when  De  Vries'  investigations  were  published  the  time  was  ripe  for 
their  general  appreciation. 

The  data  from  which  De  Vries  evolved  his  theory  is  thought  to 
%how  not  only  that  mutations  are  a  class  of  variations  useful  as  a 
factor  in  evolution,  but  that  they  are  the  only  possible  way  by 
which  evolution  could  take  place.  Whether  this  is  true  or  npt 
is  not  possible  at  present  to  determine;    but  we  can  say  that 


LATER    EVOLUTIONARY   THEORIES    AND    PRINCIPLES.  3 1 

the  rapidly  increasing  volume  of  data  points  toward  this  conclu- 
sion. Moreover,  there  is  no  experimental  data  at  hand  to  refute 
this  view.  The  mutation  theory  certainly  does  clear  up  many  of 
the  points  which  did  not  seem  to  be  clearly  explained  from  Dar- 
win's point  of  view.  We  will  endeavor  to  give  an  outline  of  the 
chief  points  involved. 

In  the  middle  of  the  eighteenth  century,  Linnaeus,  the  great 
Swedish  botanist,  introduced  our  present  system  of  classifying 
plants  and  animals.  He  used  two  names :  a  species  name  or  name 
of  a  group  of  individuals  which  were  fairly  constant  and  alike 
in  their  characters  and  which  differed  from  other  related  groups 
by  characters  which  could  be  recognized  from  descriptions  ;  and  a 
generic  name  which  included  related  groups  of  these  species  in 
a  broader  class  called  a  genus.  He  supposed  that  his  species 
were  the  units  of  nature  and  were  created  as  such  in  the  begin- 
ning. He  did  recognize  subdivisions  of  species  which  he  called 
varieties  but  had  no  very  clear  ideas  concerning  them.  The 
object  of  his  work  was  to  bring  into  some  order  the  plants  then 
known,  and  not  to  study  lesser  divisions. 

The  classifying  of  species  has  since  been  more  or  less  a  series 
'of  individual  judgments  of  different  botanists;  some  used  more 
definite  characters  as  distinctions  between  species,  and  made  a 
small  number  of  species,  while  others  used  fewer  or  smaller  dis- 
tinctions and  described  four  or  five  times  as  many  species  in  the 
same  genus. 

More  recently  Jordan,  a  French  botanist,  became  satisfied  that 
the  only  reasonable  way  to  classify  species  was  to  grow  a  large 
number  of  individuals  and  study  the  characteristic  differences 
between  them.  When  this  was  done,  he  found  that  while  some 
of  Linnaeus'  species  were  relatively  uniform,  others  contained 
many  groups  of  plants  which  differed  from  each  other  by  one  or 
more  constant  characters.  Often  these  differences  were  in  parts 
of  the  plant  which  would  remain  unnoticed  by  the  untrained  eye, 
but  still  the  differences  were  there  and  were  transmitted  to  the 
succeeding  generations. 

De  Vries  has  called  these  groups  of  plants,  "elementary  species." 
His  idea  is  that  plants  and  animals  are  made  up  of  thousands  of 
large  or  small,  but  distinct  heritable  characters ;  and  that  these 
characters  have  arisen,  one  or  more  at  a  time,  fully  formed  and 
able  to  function,  from  parents  which  did  not  possess  the  characters. 
5 


32  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    1 58. 

It  is  recognized  that  some  plants  are  much  more  variable  in  this 
respect  than  others :  the  common  whitlow  grass  (Draba  verna) 
has  had  several  hundred  of  these  elementary  species  described, 
while  others  of  Linnaeus'  species  seem  to  vary  only  with  the 
common  fluctuating  variation.  This  phenomenon  is  explained  by 
the  hypothesis  that  there  are  periods  when  a  species  is  producing 
mutations  and  other  periods  when  mutations  very  rarely  if  ever 
appear.  These  periods  may  be  hundreds  of  years  apart  and  thus 
account  for  the  apparent  constancy  of  some  species  such  as  wheat, 
of  which  we  have  a  long  history  under  domestication. 

In  making  culture  studies  of  many  species  of  plants,  these 
elementary  species  have  been  found  very  common  indeed,  but 
no  one  -had  seen  a  new  form  originate  from  an  older  wild  one 
until  De  Vries  had  the  good  fortune.  It  is  true  that  many  wide 
mutations,  or  jumps  of  a  distinct  kind,  had  been  isolated  among 
cultivated  plants,  and  were  called  "sports"  by  horticulturists. 
De  Vries,  however,  discovered  and  propagated  a  series  of  interest- 
ing mutations  from  a  plant  growing  wild  on  some  fields  near 
Amsterdam. 

The  plant  which  was  caught  in  the  act  of  originating  a  new 
species  is  an  American  plant  of  the  evening  primrose  family 
known  as  CEnothera  Lamarkiana.  It  had  been  cultivated  in  Hol- 
land many  years  but  had  escaped  from  cultivation  and  had  been 
growing  wild  for  a  long  time.  On  closely  examining  these  plants, 
De  Vries  discovered  two  new  and  unknown  forms  that  were 
quite  unlike  the  remainder  of  the  plants  which  were  typical  of 
the  species.  Each  of  these  types  occurred  in  spots,  as  if  they 
had  arisen  as  the  offspring  of  a  single  plant.  Fortunately, 
De  Vries  was  not  satisfied  with  the  single  observation,  but  took 
seed  and  roots  of  a  number  of  the  plants  of  each  type  and  grew 
them  in  his  garden  for  a  number  of  generations.  In  all,  he 
cultivated  at  least  50,000  plants,  and  among  this  number  about 
800  were  found  which  differed  distinctly  from  the  parent  species, 
and  whose  characters  were  constant  when  reproduced  by  self- 
fertilization.  That  is,  he  was  able  to  obtain  from  one  to  three 
per  cent,  of  new  and  distinct  forms  which  did  not  tend  to  go  back 
to  the  parent  form  but  to  remain  constant.  One  of  the  forms 
was  a  giant  form  with  large  flowers ;  one  was  a  dwarf  form ;  in 
one  the  ovules  were  imperfect;  and  another  had  defective  pollen. 
The  last  two  forms  were  evidently  less  fitted  for  existence  than 
the  parent   form  and  were   raised  with   difficulty,   while   other 


LATER   EVOLUTIONARY   THEORIES    AND    PRINCIPLES.  ;i^ 

forms  were  able  to  survive  in  natural  competition  with  the 
parent  species. 

These  new  forms  corresponded  to  the  elementary  species  that 
had  been  observed  before  in  nature,  but  had'  never  been  seen  to 
arise.  Each  character  had  the  common  fluctuating  variability 
which  often  made  the  fluctuation  of  two  forms  overlap,  for 
instance  the  longest  leaves  of  the  short  form  being  longer  than 
the  shortest  leaves  of  the  long  form.  But  in  each  of  these  cases, 
Avhen  the  two  forms  were  cultivated  separately,  the  variability  was 
found  to  group  itself  around  a  typical  point  and  to  be  distinct  in 
each  form. 

We  cannot  go  deeply  into  the  numerous  questions  regarding 
variability  and  inheritance  upon  which  these  experiments  have 
shown  light,  but  it  may  be  well  to  sum  up  some  of  the  chief  points. 

1.  Mutations  are  not  so  rare  as  was  formerly  supposed.  They 
are  found  in  wild  as  well  as  cultivated  plants.  Their  occurrence 
reasonably  accounts  for  the  numerous  "elementary  species,"  or 
subdivisions  of  Linnaeus'  species  that  are  found  in  nature. 

2.  Mutations  are  constant  in  succeeding  generations  and  thus 
account  for  the  constancy  in  nature  of  these  elementary  species. 
The  tendency  of  the  progeny  of  extreme  fluctuating  variations  to 
return  to  the  original  type  appears  to  make  continuous  evolu- 
tion impossible,  but  with  mutations  which  remain  constant  until 
succeeded  by  other  mutations,  there  is  no  such  difficulty. 

3.  The  criticism  that  imperfect  and  rudimentary  characters 
would  not  survive  by  natural  selection,  is  here  valueless,  for 
mutations  appear  fully  formed. 

4.  Anticipating  the  text  a  little,  we  may  state  that  Mendel's 
work  on  heredity  has  shown  that  mutations  would  not  neces- 
sarily be  swamped  by  intercrossing  with  the  parent  kind,  even 
if  they  occurred  singly.  It  may  also  be  deduced  from  his  work 
that  useless  characters  may  survive. 

5.  De  Vries'  work  shows  that  in  the  working  of  the  principle 
of  natural  selection,  it  is  more  likely  a  contest  in  which  the 
fittest  elementary  species  survives.  The  contest  for  survival 
among  individuals  due  to  fluctuating  variations  has  not  yet  been 
shown  to  produce  permanent  changes.  Possibly  this  would  be 
done,  however,  if  we  imagine  a  gradually  but  permanently  chang- 
ing environment  to  which  individual  organisms  adapt  themselves 
in  different  degrees. 


34  CONNECTICUT   EXPERIMENT   STATION    BULLETIN    1 58. 

6.  By  mutations,  it  is  believed  that  evolution  may  have  been 
accomplished  in  the  time  allotted  for  its  action  by  the  calculations 
of  the  physicists  and  geologists. 

From  this  discussion  we  can  see  that  whether  or  not  we  accept 
De  Vries'  theory  as  proven*  in  its  entirety ;  nevertheless  as  a 
theory  it  explains  reasonably  and  clearly  the  majority  of  the  perti- 
nent criticisms  of  the  theory  of  evolution  by  the  selection  of 
fluctuating  variations,  which  were  given  at  the  end  of  the  first 
chapter. 

According  to  De  Vries,  there  are  three  classes  of  mutations, 
progressive,  degressive  and  retrogressive.  If  an  entirely  new 
character  appears  in  an  organism,  it  is  a  progressive  mutation. 
It  is  thought  that  this  class  has  been  the  great  factor  in  evolu- 
tion. The  degressive  mutations  are  those  which  occur  when  a 
character  appears  that  has  been  partially  latentf  or  hidden. 
A  retrogressive  mutation  is  when  a  character  previously  active 
becomes  latent,  as  when  a  species  that  has  always  produced 
colored  flowers  suddenly  produces  a  white  variety. 

A  mutation  is  held  to  be  the  appearance  or  disappearance  of  a 
distinct  heritable  character.  De  Vries  disclaims  any  idea  that 
these  changes  must  be  wide,  but  they  must  be  distinct  in  that  there 
in  a  change  of  type  in  the  variation  which  is  inherited.  The 
mutation  may  be  within  the  limits  of  a  fluctuation,  but  still  be  a 
true  mutation.  To  illustrate  this,  cut-leaved  plants  of  a  number 
of  species  have  appeared  as  mutations,  but  there  may  be  individual 
leaves  of  the  ordinary  types  which  have  as  deep  or  deeper 
incisions  through  fluctuating  variations  than  have  the  least  incised 
individuals  of  the  cut-leaved  type.  It  has  been  customary  to 
regard  mutations  as  sufficiently  definite  changes  in  botanical 
characters  that  they  may  be  recognized  when  grown  in  pedigree 


*  There  are  points  concerning  the  germ  cell  structure  of  De  Vries' 
primrose  mutations,  and  the  fact  that  certain  of  these  aberrant  forms 
have  continued  to  give  off  mutations,  that  make  it  a  question  if  these 
cultures  were  not  either  hybrid  forms,  or  parthenogenetic  forms  (forms 
in  which  the  seeds  develop  without  fertilization).  The  original  wild 
plant  seems  to  have  disappeared  in  America,  hence  experiments  with  it 
to  determine  these  points  cannot  be  made.  Nevertheless,  even  if  the 
primrose  mutations  should  be  otherwise  explained,  it  would  not  affect 
the  general  theory  of  the  discontinuity  of  heritable  characters.  Other 
data  presented  by  Bateson,  De  Vries  and  others,  are  more  convincing 
to  my  mind,  than  are  the  primrose  experiments ;  although  the  latter 
have  been  received  with  greater  popular  acclaim. 

t  Latent  is  a  term  used  to  explain  the  condition  of  a  character  that 
appears  to  be  lost,  but  is  only  obscured  or  hidden. 


LATER    EVOLUTIONARY    THEORIES    AND    PRINCIPLES.  35 

cultures ;  that  is  when  isolated  and  reproduced  in  pure  lines  for 
several  generations.  Doubtless  with  sufficiently  accurate  methods 
this  could  always  be  done.  But  it  does  not  seem  to  be  a  necessary 
part  of  the  theory  to  regard  mutations  as  additions  or  subtrac- 
tions of  what  are  generally  regarded  as  specific  characters.  If 
mutations  may  appear  in  any  direction,  I  see  no  reason  why  they 
may  not  sometimes  appear  as  linear  changes  (plus  or  minus)  of 
characters  already  present.  Johannsen's  results  might  then  be 
interpreted  as  mutations  in  which  the  real  unit  characters  are 
portions  or  segments  of  what  visibly  appears  as  the  character,  but 
differing  from  fluctuations  of  the  same  character  by  the  constancy 
with  which  they  are  reproduced.  A  perfectly  isolated  line  con- 
taining only  a  definite  number  of  segments  of  the  character  in 
their  germ  cells,  would  remain  true  to  its  own  type  in  succeeding 
generations  of  progeny.  The  difficulty  in  isolating  a  pure  line  is 
that  the  fluctuations  of  different  lines  overlap  and  are  indistin- 
guishable in  appearance. 

If  we  regard  the  growing  sugar  beet  as  containing  a  chemical 
laboratory  for  the  manufacture  of  sugar,  we  may  imagine 
changes  taking  place  in  the  germ  cells  from  which  an  apparatus 
and  reagents  appear  by  which  a  higher  or  lower  amount  of  sugar 
would  normally  be  produced.  But  grouped  about  this  normal  type 
would  be  fluctuating  variations  due  to  environment.  In  other 
words,  there  might  be  germinal  or  genetic  variations  of  the 
sugar-producing  character,  a  pure  line  from  which  would  nor- 
mally produce  beets  with  12  per  cent,  sugar,  but  with  fluctuating 
variations  of  from  10  per  cent,  to  14  per  cent,  sugar.  Another 
pure  line  might  normally  produce  10  per  cent,  sugar  with  fluc- 
tuations of  from  8  per  cent,  to  12  per  cent. 


36  CONNECTICUT    EXPERIMENT   STATION    BULLETIN    1 58. 

III. 

Heredity. 

Through  common  usage,  the  term  heredity  brings  to  our  minds 
a  more  or  less  definite  meaning,  but  a  precise  definition  is  diffi- 
cult. Suppose  we  say  that  it  is  the  tendency  of  the  characters  of 
blood  relations  toward  duplication.  Variation,  which  we  have 
just  been  discussing,  and  heredity  are  in  one  sense  opposite  in 
their  meaning.  If  nothing  interfered,  and  inheritance  were 
perfect,  there  would  be  no  variation  and  hence  no  evolution; 
differences  in  species  would  necessarily  be  due  to  direct  creation, 
or  spontaneous  generation,  and  each  species  would  be  made  up 
of  individuals  exactly  alike.  On  the  other  hand,  we  could 
hardly  imagine  the  chaos  if  there  were  no  limits  to  variation. 
Heredity  and  variation  have  been  spoken  of  as  two  opposed 
forces,  the  first  a  centripetal  force  which  is  striving  to  keep 
nature  fixed  within  due  bounds,  and  the  second  a  centrifugal 
force  which  is  continually  striving  to  overleap  these  bounds. 
The  continued  working  of  these  two  forces  under  laws  of  which 
we  as  yet  know  little,  has  built  up  the  organic  world  which 
surrounds  us. 

Blended  Inheritance. 

Of  the  mechanism  of  bisexual  inheritance  very  little  is  known, 
but  from  observation  of  its  results  it  has  been  divided  into 
blended,  mosaic  and  alternate  inheritance.  Blended  inheritance 
is  where  there  is  a  fusion  of  two  characters,  so  that  a  character 
possessed  by  an  offspring  appears  to  be  an  average  of  the  two 
characters  as  possessed  by  the  parents.  The  most  familiar  case 
of  blended  inheritance  is  the  mulatto — the  result  of  the  union 
of  a  white  an-d  a  black  individual  of  the  human  race.  The 
mulatto  is  intermediate  between  the  two  colors,  and  breeds  true 
for  generation  after  generation.  If  the  mulatto  is  crossed  again 
with  white  or  black  stock,  the  resulting  offspring  is  correspond- 
ingly whiter  or  blacker. 

Cases  of  blended  inheritance  are  found  in  all  sorts  of  crosses,— 
those  between  races,  varieties  and  elementary  species.  It  has 
been  thought  to  be  a  characteristic  occurrence  in  hybridization 
between  different  Linnean  species,  but  it  is  now  known  that  even 
here  the  other  forms  of  inheritance  occur.     No  general  law  for 


HEREDITY.  37 

the  mechanism  of  blended  inheritance  has  been  found,  but  Gal- 
ton's  law  of  ancestral  inheritances  as  mentioned  in  the  last  chap- 
ter gives  the  expectation  of  average  ancestral  resemblance  in 
the  different  generations.  This  law  is  thought  to  apply  especially 
to  blended  inheritance,  but  there  is  no  reason  why  it  could  not 
apply  to  all  forms  of  inheritance  if  we  consider  the  total  sum  of 
characters  of  an  individual  and  not  a  single  character. 

It  is  particularly  in  blended  inheritance  that  the  phenomenon 
of  prepotency*  has  been  noticed.  This  is  the  tendency  of  one  of 
the  parents  of  a  cross  to  have  more  of  its  characters  reproduced 
than  would  be  normally  expected.  It  is  stated  that  in  the  .pro- 
duction of  the  mule  the  characters  of  the  ass  are  prepotent,  while 
in  crosses  between  the  dog  and  the  jackal  the  latter  is  prepotent. 
It  is  variously  stated  that  iti  crossing  plants,  the  characters  of 
the  older  species  are  prepotent,  and  that  progressive  mutations 
are  prepotent.  Accepting  the  mutation  theory  of  evolution  as 
true,  these  two  statements  are  in  direct  opposition  to  each  other. 
We  should  be  cautious  about  accepting  any  theories  concerning 
prepotency  until  we  know  more  about  the  subject. 

Mosaic  hiheritance. 
The  most  familiar  example  of  mosaic  inheritance  is  where 
animals  of  different  coat  colors  are  bred  together.  We  some- 
times get  an  individual  that  is  piebald.  The  characteristic  colors 
of  the  two  parents  are  inherited  by  the  offspring  in  patches  on 
different  parts  of  the  body.  These  spotted  races  have  originated 
among  almost  all  of  our  domestic  animals  and  are  noticeable  in 
many  of  our  flowering  plants.  In  some  cases  they  may  be  muta- 
tions that  breed  true,  as  is  believed  by  Cuenot,  but  it  is  most 
generally  thought  that  this  is  only  a  special  form  of  alternate 
inheritance  and  that  it  will  be  explained  later  on  that  basis. 

Alternate  Inheritance  and  Mendelism. 
It  is  upon  alternate  inheritance  that  results  of  greatest  value 
have  been  obtained.  By  this  term  are  designated  numerous  cases 
in  which  a  character  of.  one  parent  is  inherited,  apparently  to  the 
complete  exclusion  of  any  influence  of  the  other  parent  on  this 
character.  Data  now  being  obtained  by  investigators  indicate 
that  this  exclusion  is  sometimes  an  exclusion  of  appearance  and 

*  It  may  be  that  prepotency  will  later  be  explained  as  due  entirely  to 
dominance  of  characters.     (See  Mendelian  Inheritance.) 


38  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    I58. 

function,  and  that  the  alternate  character  may  yet  appear  in  sub- 
sequent progeny  under  certain  conditions.  The  classical  example 
of  this  type  of  inheritance  is  that  of  eye  color  in  the  human  race. 
It  is  a  matter  of  common  observation  that  the  offspring  from  a 
union  of  a  brown-eyed  parent  and  a  blue-eyed  parent  is  never  a 
mixture  or  blend  of  the  two ;  the  children  are  either  brown-eyed 
or  blue-eyed  like  one  or  the  other  of  the  parents.  Until  1900 
this  type  of  inheritance  was  thought  to  be  comparatively  rare.  In 
that  year,  however,  it  was  discovered  by  workers  in  heredity  in 
three  different  parts  of  the  world,  that  two  laws  of  the  utmost 
importance  to  both  science  and  practice  had  been  buried  in  the 
oblivion  of  an  unnoticed  journal  for  a  whole  generation.  These 
laws  are  now  known  as  Mendel's  laws. 

Gregor  Johann  Mendel  was  an  Austrian  priest,  a  teacher  of 
physics  and  natural  science  in  the  Cloister  at  Briinn.  He  was 
appointed  Abbot  at  Briinn,  about  1869,  and  unfortunately  for 
science  he  had  little  time  left  from  his  executive  duties  for  the 
pursuance  of  his  studies.  He  died  in  1884  practically  unknown  to 
the  world.  It  was  not  until  sixteen  years  after  his  death  that 
it  became  widely  known  that  in  1865  he  had  reported  a  paper 
giving  results  of  ten  years'  expifcriments  on  inheritance, — results 
that  were  fundamental  and  epoch  making. 

By  a  wonderful  foresight,  he  perceived  that  if  progress  was 
to  be  made  in  the  study  of  heredity  the  problem  must  be  simplified 
as  much  as  possible.  It  was  the  simplicity  of  his  experiments  that 
crowned  them  with  success.  There  were  two  things  especially 
necessary  to  be  controlled,  namely,  accidental  mixtures  due  to 
crossing,  and  differences  in  too  many  characters.  The  common 
garden  pea  fulfilled  these  demands.  It  could  be  self-fertilized 
generation  after  generation  without  deterioration,  and  varieties 
were  found  that  differed  from  each  other  in  but  few  characters. 
Mendel  selected  varieties  of  the  pea  which  differed  from  each 
other  in  such  characters  as  "round  or  wrinkled  seeds,"  "yellow  or 
green  cotyledons"  or  seed  leaves,  and  "purple  or  white  flowers." 
These  varieties  he  found  to  be  true  to  their  characters  by  inbreed- 
ing. He  then  crossed  them  once  and  made  careful  records 
of  their  progeny  when  inbred  for  a  number  of  succeeding 
generations. 

He  crossed  a  yellow  seeded  variety  with  pollen  from  a  green 
seeded  variety,  and  again  crossed  the  green  seeded  variety  with 
pollen  from  that  bearing  yellow,  seeds.     It  was  found  that  it  made 


HEREDITY.  39 

no  difference  which  variety  was  used  as  the  pollen  parent  and 
♦  which  as  the  seed  parent,  the  seeds  resulting  from  the  cross  were 
in  every  case  yellow.  He  called  the  yellow  color  the  dominant 
color  and  the  green  color  the  recessive  because  it  had  receded  from 
sight  for  a  time. 

These  yellow  seeds  were  planted  the  next  season  and  the  blos- 
soms were  allowed  to  self-fertilize,  that  is,  pollen  from  the 
stamens  of  a  flower  was  allowed  to  fertilize  the  pistils  of  the 
same  flower.  It  was  found  that  all  of  the  plants  bore  both 
yellow  and  green  seeds,  frequently  both  colors  being  found  in  the 
same  pod.  This  proved  that  although  the  seeds  from  the  cross 
were  in  the  first  generation  all  yellow  in  color,  the  green  color 
was  still  there  potentially,  waiting  to  appear  in  the  next 
generation.  Continuing  the  work  for  the  third  generation,  he 
found  that  all  of  the  plants  from  green  seeds,  when  allowed  to 
self-fertilize,  produced  green  seeds  entirely.  This  was  continued 
for  six  generations  with  no  reapipearance  of  the  yellow  character. 
In  other  words,  the  recessive  character  bred  true. 

When  the  same  method  of  inbreeding  was  used  on  the  yellow 
seeded  progeny  of  the  gross,  however,  a  different  result  was 
obtained.  Some  of  the  plants  were  found,  when  self-fertilized, 
to  produce  both  yellow  and  green  seeds  just  as  their  parents  had 
done,  while  others  bred  true  in  succeeding  generations.  That 
is,  some  of  these  yellow  seeds  were  "pure"  yellow  seeds,  while 
others  were  "hybrid"  yellow  seeds  like  the  parents.  But  in  the 
case  of  the  hybrid  yellow  seeds,  the  yellow  color  was  still 
dominant;  that  is,  it  was  apparent  to  the  eye;  while  the  green 
color  was  recessive  or  hidden.  Moreover,  long  continued  experi- 
ments showed  that  there  was  a  constant  numerical  ratio  between 
the  yellow  and  green  seeds,  which  is  illustrated  by  the  following 
table. 

yellow  X  green  (or  vice  versa) 
ist  gen.  all  yellow 

I 
2d  gen.  75^  yellow  to 25^  green 

\  I 

3d  gen.  2S%  50^  25^  f 

pure  yellow  to hybrid  yellow  to pure  green       pure  green 

4th  gen.  pure  yellow  25^          50^          25^  pure  green  pure  green 

^               pure hybrid — pure            -^  '-^ 

pure  yellow  yellow     yellow    green  pure  green  pure  green 
6 


40  CONNECTICUT   EXPERIMENT    STATION    BULLETIN    1 58. 

His  results  may  be  stated  as  follows : 

If  two  contrasted  characters  which  have  previously  bred  true 
are  crossed,  one  only,  the  dominant  character,  appears  in  the 
hybrid.     (The  Law  of  Dominance.) 

Second,  in  succeeding  g-enerations,  self-fertilized  plants  grown 
from  seeds  of  this  cross  reproduce  both  characters  in  the  pro- 
portion o"f  three  of  the  dominant  character  to  one  of  the  recessive 
character.  Furthermore,  the  recessive  character  continues  ever 
after  to  breed  true,  whiTe  those  plants  bearing  the  dominant  char- 
acter are  one-third  pure  dominants  which  ever  after  breed  true  to 
the  dominant  character,  and  two-thirds  hybrid  dominants  which 
contain  the  recessive  character  in  a  hidden  condition.  (Mendel's 
law  of  inheritance.)  Using  D  to  represent  the"  dominant  charac- 
ter and  R  to  represent  the  recessive  character,  the  working  of  the 
law  may  be  thus  illustrated: 

D  R 

\     ./ 

^^^         DR         ^\\ 
D-"  /-  I    I  \-^«  \R 

°   r  /f i\  ^  ^\ 

D  D      D      DR      R       R         R 

Mendel  did  not  claim  that  this  law  of  inheritance  holds  good 
for  all  organisms  or  even  for  all  plants,  but  it  is  now  being  cor- 
roborated for  an  ever  increasing  number  of  characters  in  both 
plants  and  animals.  Even  the  results  which  he  obtained  did  not 
follow  the  exact  numerical  ratio  just  given  but  were  sufficiently 
exact  for  him  to  formulate  a  theory  to  account  for  the  observed 
facts. 

The  theory  supposes  that  when  a  dominant  and  a  recessive 
character  meet  in  a  cross,  the  germ  cells  which  are  produced 
in  the  hybrid  do  not  blend  these  characters  but  possess  either  the 
one  or  the  other ;  and  as  the  possession  of  either  character  is  a 
matter  of  chance,  on  the  average  50  per  cent,  of  the  germ  cells 
will  bear  the  dominant  character  and  50  per  cent,  will  bear  the 
recessive  character.  In  a  plant,  for  example,  50  per  cent,  of  the  - 
pollen  cells  would  bear  the  "dominant  and  the  other  50  per  cent, 
would  boar  the  recessive  character.  The  t.g%  cells  would  like- 
wise one-half  contain  the  dominant  character  and  one-half  the 
recessive  character. 


HEREDITY.  4 1 

Now  if  we  could  pick  out  at  random  any  one  hundred  pollen  or 
male  cells  to  fertilize  any  one  hundred  egg  or  female  cells,  we 
can  see  that  there  are  equal  chances  for  four  results.  A  D  male 
cell  might  meet  a  D  female  cell,  a  D  male  cell  an  R  female  cell, 
an  R  male  cell  a  D  female  cell,  and  an  R  male  cell  an  R  female 
cell.     In  an  abbreviated  form  it  amounts  to  this : 


D- 

-^D 

Male 

D^ 

^D 

Female 

cells 

R-- 

^\  R 

cells 

R- 

-^R 

We  have  (D  +  D),  (0  +  R),  (R  +  D)  and  (R  +  R)  formed 
in  equal  quantities,  but  as  the  two  middle  terms  are  the  same,  we 
can  reduce  the  formula  to  one  (D  -)-  D)  to  two  (D  -f-  R)  to  one 
(R-|-  R).  But  wherever  there  is  a  D  present  in  the  germ  cell, 
the  dominant  character  shows  while  the  recessive  character  is 
hidden.  The  one  part  or  the  25  per  cent,  of  the  individuals 
showing  the  character  (D  -f-  D)  will  appear  to  be  just  like  the  two 
parts  or  50  per  cent,  of  the  individuals  having  the  character 
(D  -|-  R).  Therefore  there  will  be  75  per  cent,  of  the  individuals 
which  will  show  the  dominant  or  D  character  while  25  per  cent, 
will  show  the  recessive  or  R  character.  These  25  per  cent,  show- 
ing the  R  character  will  ever  after  breed  true  because  they  contain 
nothing  but'  the  recessive  character,  while  of  the  75  per  cent, 
showing  the  dominant  character,  one-third  or  those  having  the 
pure  (D  -^  D)  character  will  breed  true  in  succeeding  genera- 
tions while  the  other  two-thirds  having  the  (D  -j-  R)  or  hybrid 
character  will  again  split  in  the  next  generation. 

Of  course  it  is  only  theoretically  that  these  ratios  are  exact. 
They  increase  in  accuracy  with  larger  numbers.  If  one  thousand 
seeds  were  counted  in  the  second  generation,  they  would  come 
nearer  the  proportion  of  three  to  one  (3D  to  iR)  than  if  one 
hundred  were  counted.  As  a  tangible  illustration  of  what  may 
be  expected  in  practical  work,  take  one  hundred  black  beans  and 
one  hundred  white  beans  and  shake  them  up  in  a  hat.  Now  draw 
them  out  in  pairs,  and  see  what  combinations  you  'get.  In  an 
actual  count  I  obtained  the  following  results. 


Actual 
number 

Theoretics 
number 

22 

55 
23 

2  black 

•I  black,  I  white 

2  white 

25 
50 
25 

42  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    1 58. 

This  explains  why  the  practical  work  is  not  in  exact  accord 
with  the  theory.  The  actual  results  approach  nearer  and  nearer 
to  the  theory  as  larger  and  larger  numbers  are  used. 

Mendel  was  not  content  with  experiments  in  which  only  one  pair 
of  differentiating  characters  were  concerned.  He  made  crosses 
in  which  two  and  three  pairs  of  characters  were  associated  and 
found  that  they  independently  obeyed  the  same  laws.  Taking  two 
pairs  of  characters,  he  designates  the  dominant  characters  as  A 
and  B  and  the  recessive  characters  as  a  and  b.  The  characters 
crossed  were  as  follows  : 

Seed  parent   )  A  form  round  Pollen  parent  j  ,     „„ji^  ^    „i 

A  o          ■{  D        J  1     r      1          11  u              i  o  seed-leaf  color 

AB           I  D  seed-leaf  color  yellow  ab              i 

{                                  ^  (       green 

When  these  two   forms  were  crossed  all  of  the  hybrid  seeds 

appeared  round  and  yellow  (AB)  like  those  of  the  seed  parent, 

that  is,  the  round  and  yellow  forms  were  dominant. 

When  these  seeds  were  sown  and  the  plants  self- fertilized,  four 

kinds   of   seeds   appeared   in  the   four  combinations   that   were 

possible ;   and  with  the  following  numbers  of  each : 

AB  round  and  yellow   31S 

aB    angular  and  yellow    loi 

Ab    round  and  green  108 

ab    angular  and  green  . .' 32 

These  figures  stand  approximately  in  the  relation  of  9AB  to 

3Ab  to  3aB  to  lab :    but  these  forms  which  appeared  to  be  of 

only  four  classes  were  found  in  the  next  generation  to  be  made 

up  of  nine  really  different  classes. 

From  the  round  yellow  seeds  (apparently  AB)  were  obtained: 

(i)  AB       round  and  yellow  seeds  38 

(2)  ABb     round  yellow  and    green  seeds 65 

(3)  AaB     round  yellow    and   angular  seeds 60 

(4)  AaBb  round  yellow  and  green,  angular  yellow  and  green  seeds  138 

From  the  round  and  green  seeds  (apparently  Ab)  were 
obtained : 

(5)  Ab       round  green  seeds    35 

(6)  Aab     round  angular  and  green  seeds  67 

From  the  angular  and  yellow  seeds  (apparently  aB)  were 
obtained : 

(7)  aB       angular  and  yellow  seeds    28 

(8)  aBb     angular  and  yellow  green  seeds    67 

From  the  angular  and  green  seeds  (ab)  were  obtained: 

(9)  ab        angular  and  green  seeds    30 


HEREDITY. 


43 


We  notice  that  there  were  nine  classes  of  individuals  produced 
whose  characters  had  the  formulae  given  above.  This  was 
experimentally  proved.  The  forms  AB,  Ab,  aB  and  ab  were 
found  to  be  true  and  did  not  afterwards  vary.  The  hybrid 
character  of  the  remaining  classes  was  subsequently  shown. 

The  numerical  relations  found  were  approximately  the  following 
series.  AB,  Ab,  aB,  ab,  2ABb,  2aBb,  2Aab,  2AaB  and  4AaBb. 
This  is  really  a  combination  by  multiplication  of  the  two  series, — 

(A  +  2Aa  +  a)x(B  +  2Bb  +  b)  =  AB  +  Ab  +  aB  +  ab  + 

2ABb  +  2aBb  +  2Aab  +  2  AaB  +  4AaBb.* 

The  two  pairs  of  characters  behave  independently  of  each  other 
and  as  if  chance  only  governed  their  combinations.  Moreover, 
three  pairs  of  contrasted  characters  were  found  to  behave  in 
exactly  the  same  manner,  the  number  of  forms  found  being  what 
would  theoretically  be  expected  if  the  above  product  were  multi- 
plied by  another  series  represented  by  C  -f-  2Cc  +  c. 

These  results  can  be  reduced  to  still  simpler  terms,  as  is  shown 
in  the  following  table.  Let  n  represent  ttie  number  of  pairs  of 
contrasted  characters  in  the  parents.  When  they  are  crossed, 
the  second  generation,  when  self-fertilized,  show  visible  differ- 
ences of  2  to  the  nth  power.  These  visibly  different  classes 
actually  contain  3  to  the  wth  power  different  classes,  the  phe- 
nomenon of  dominance  obscurity  part  of  them.  Finally  when 
crossing  to  secure  combinations  of  n  characters,  we  must  have  4 
to  the  nth  power  number  of  individuals  to  be  theoretically  certain 
of  at  least  one  individual  in  each  class. 

Mendel's  Law  of  Inheritance  of  Unit  Characters. 


No.  of  pairs  of  dif. 
between  parents. 

n 

No.  of  visibly  dif. 

classes  each  cont.  one 

pure  individual. 

2" 

No.  of  actual  classes, 
both  pure  and  hybrid. 

3"' 

Smallest  No.  of  offspring 

allowing  at  least  one 

to  a  class. 

4"' 

I 
2 

3 

4 
5 
6 

2 

4 

8 

16 
32 
64 

3 

9 

27 

81 
243 
729 

-,    Experimen- 
7  1    tally   tested 
g°  [   by    Mendel 
^■'    for  peas. 
256] 
1024  y  Calculated 
4096  J 

*  Instead  of  writing  AA  and  aa  in  the  series   one  of  the  letters  is 
dropped.  t 


44  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    I58. 

When  such  a  noteworthy  set  of  conclusions  as,  those  of  Mendel's 
is  announced  it  is  important  that  they  should  be  confirmed  by 
other  investigators.  This  has  been  done  by  investigators  in 
several  countries,  and  in  recent  years  Mendel's  laws  have  been 
found  to  hold  for  a  large  number  of  characters  in  numerous 
varieties  of  our  domestic  plants  and  animals.  Characters  in  such 
different  subjects  as  rats,  mice,  guinea  pigs,  cats,  horses,  oxen, 
poultry  and  various  insects,  among  animals ;  and  for  wheat,  oats, 
maize,  peas,  beans,  etc.,  among  plants  have  shown  Mendelian 
inheritance  in  certain  characters  in  hybrids  between  their  varieties. 
How  far  these  laws  will  be  found  to  hold,  we  do  not  know  at 
present;  but  the  number  of  cases  is  being  extended  daily.  It  is 
possible  and  even  probable  that  a  great  many  cases  which  are  now 
considered  as  blended  and  mosaic  inheritance  will  be  found  to 
obey  some  extension  of  Mendel's  law ;  when  it  is  better  under- 
stood, moreover,  it  is  quite  likely  that  many  characters  that  are 
now  regarded  as  units  will  be  finally  divided  into  several  units, 
and  their  behavior  in  different  combinations  thus  accounted  for. 
Bateson  has  already  found  that  several  characters,  such  as  certain 
colors,  which  would  at  first  thought  be  regarded  as  unit  char- 
acters, are  actually  made  up  of  two,  three  or  even  a  larger  number 
of  factors ;  and  such  facts  make  it  very  difficult  to  derive  con- 
clusions from  experimental  data  on  account  of  their  very  great 
complication.  # 

We  have  treated  Mendelism  rather  more  fully  than  blended  or 
mosaic  inheritance  because  it  is  the  only  law  of  inheritance  that 
has  been  formulated  that  will  greatly  help  the  plant  breeder. 
Galton's  law  of  ancestral  inheritance,  even  though  it  should 
finally  be  brought  into  conformity  with  Mendelian  results,  will 
probably  never  be  of  great  practical  use  because  it  will  be  much 
more  of  a  law  of  averages  within  races  than  a  law  of  expecta- 
tion from  crosses.*  '  Mendelism  has  been  treated  in  this  chapter 
just  as  the  author  himself  left  it.  In  the  next  chapter  some  of 
the  more  important  modern  results  along  Mendelian  lines  will 
be  described. 


*  Galton's   law   is   statistical  and  deals  with  averages;  Mendel's   law  is 
physiological  and  deals  with  individuals. 


METHODS    OF    PLANT    IMPROVEMENT.  45 

IV. 

Methods  of  Plant  Improvement. 

We  have  tried  to  show  that  there  are  three  main  methods  by 
which  the  numerous  improvements  in  our  cultivated  plants  and 
domestic  animals  have  been  effected.     They  are: 

1.  The  continued  selection  of  individuals  whose  desirable 
characters  have  fluctuated  above  the  average  of  their  race. 

2.  The  isolation,  from  natural  mixtures  of  several  elementary 
species,  of  those  forms  which  possess  the  most  desirable  economic 
qualities. 

3.  The  combination  of  desirable  qualities  possessed  by  dif- 
ferent related  forms,  by  means  of  hybridization. 

The  most  progressive  plant  breeders  use  all  three  methods ;  but 
these  methods  must  be  modified  to  meet  the  various  peculiarities 
of  different  kinds  of  plants.  Sometimes  free  intercrossing  or  a 
tendency  toward  sterility  in  inbred  plants  almost  prohibits  the 
complete  isolation  of  natural  forms.  In  some  cases  the  common 
method  of  propagation  is  by  buds,  and  fluctuations  can  be  multi- 
plied in  a  commercial  way.  In  other  plants  desirable  characters* 
are  possessed  by  different  types,  and  hybridization  must  be  used  to 
determine  if  certain  combinations  of  characters  will  not  produce 
the  desired  quality. 

We  cannot  take  up  any  extended  history  of  what  has  been  done 
in  plant  breeding,  for  that  would  be  to  give  the  history  of  each 
of  the  thousands  of  varieties  of  our  cultivated  plants ;  but  we  will 
give  a  number  of  typical  examples,  illustrating  what  has  been 
accomplished  by  the  use  of  these  three  lines  of  work.  The 
investigations  along  theoretical  lines  have  shown  that  there  are 
obstacles  and  limitations  belonging  to  each  class.  It  is  necessary 
to  know  how  these  facts  affect  practical  work 

The  Selection  of  Fluctuations. 

We  have  already  mentioned  the  sugar  beet  as  an  example  of  a 
crop  in  which  fluctuating  variations  have  been  selected  for  a  long 
term  of  years.  We  do  not  know  just  how  much  progress  was 
made,  if  any,  irl  raising  the  sugar  content  of  the  sugar  beet 
previous  to  the  middle  of  the  nineteenth  century.     The  beginning 


46  CONNECTICUT   EXPERIMENT    STATION    BULLETIN    1 58. 

of  its  culture  for  sugar  purposes  was  about  the  year  eighteen 
hundred.  Experiments  were  carried  on  in  both  Germany  and 
France,  and  even  with  the  very  imperfect  methods  of  the  time, 
6  per  cent,  of  sugar  was  often  obtained.  What  the  fluctuations 
in  sugar  content  of  individual  beets  were  at  that  time  we  do  not 
know,  for  modern  and  accurate  methods  of  sugar  determinations 
in  beets  have  been  in  use  only  for  a  generation.  Previous  to 
the  time  of  Louis  Vilmorin,  about  1850,  there  had  been  some 
few  selections  of  mother  beets  for  higher  sugar  content  by  plac- 
ing the  roots  in  solutions  of  different  density  and  selecting  those 
having  the  highest  specific  gravity.  There  was  probably  little 
improvement  made  in  this  manner,  for  the  frequent  formation 
of  hollows  in  the  centre  of  the  root  introduces  large  errors  in  such 
determinations.  Louis  Vilmorin  recognized  the  fault  in  this 
method  and  began  the  first  real  selection  of  mother  beets  for 
higher  sugar  content  by  pressing  out  the  juice  from  a  section  of 
the  beet,  making  density  or  specific  gravity  determinations  upon 
the  juice  itself  and  planting  the  mother  beets  whose  superiority 
was  thus  shown. 

Later  the  improvement  of  chemical  methods  of  analysis,  includ- 
ing the  use  of  the  polariscope,  has  made  rapid  determinations  of 
sugar  possible.  At  present  there  are  German  and  French  seed 
growers  that  make  as  many  as  100,000  sugar  determinations  upon 
individual  beets  ever  year.  Their  method  is  to  take  a  cylindrical 
piece  cut  from  the  beet  in  a  diagonal.  In  this  way  a  fair  sample 
is  taken,  for  different  cross  sections  of  the  roots  vary  in  their 
sugar  content.  After  these  cylinders  from  all  of  the  beets  are 
analyzed,  the  best  are  selected  and  are  carefully  saved  until  next 
season,  when  they  are  planted  to  produce  seed  for  the  commercial 
growers. 

As  early  as  1878,  the  time  of  the  Paris  Exhibition,  we  have 
records  of  varietiesithat  averaged  16  per  cent,  to  18  per  cent,  sugar 
and  whose  individual  beets  ran  as  high  as  25  to  28  per  cent. 
Since  that  time  thirty  years  of  continuous  selection  has  made  no 
progress.  Our  commercial  beet  races  are  kept  up  to  about  16 
per  cent,  by  annual  selections  from  large  numbers  of  mothers 
of  known  composition,  but  it  is  impossible  to  reach  a  higher 
average.  The  fluctuations  are  practically  the  ^same  as  we  find 
in  our  earliest  records.     Apparently  no  mutations  have  intervened, 


METHODS    OF    PLANT    IMPROVEMENT.  47 

and  the  best  strains  of  belts  have  been  fairly  well  isolated.  Now 
all  that  selection  is  doing-  is  to  perpetuate  these  improved 
races.  Beets  are  open  fertilized,  that  is,  they  cross-fertilize 
naturally  in  the  field,  hence  the  continuous  need  of  careful  selec- 
tion to  keep  their  sugar  content  up  to  the  standard  reached  a 
generation  ago.  It  has  been  definitely  shown  that  without  tliis 
continuous  selection  their  constant  intercrossing  with  inferior 
blood  that  still  remains,  will  immediately  make  them  regress 
toward  the  old  average  of  sugar  content  of  a  hundred  years  past. 
Possibly  there  are  causes  contributory  to  this  regression,  but  it 
can  hardly  be  doubted  that  they  would  reach  this  average  in  a 
very  few  years  if  selection  ceased. 

Work  analogous  to  raising  the  sugar  content  of  the  sugar  beet 
has  been  going  on  in  this  country  for  the  past  ten  years.  -  I  refer 
to  the  work  of  Hopkins  and  his  associates  at  the  Illinois 
Agricultural  Experiment  Station  in  changing  the  composition  of 
the  maize  kernel.  With  this  work  the  writer  had  the  pleasure 
to  have  been  connected  for  five  years. 

Work  was  started  in  1896  to  change  the  composition  of  the 
maize  kernel  along  four  different  lines,  for  higher  and  lower 
protein,  and  for  higher  and  lower  oil  contents.  One  hundred 
sixty- three  individual  ears  of  Burr's  White  maize  from  the  1896 
crop  were  analyzed  and  the  proper  selections  in  each  case  planted 
in  their  respective  plots.  In  each  plot  from  twelve  to  twenty-four 
rows  were  planted  and  each  row  contained  only  the  kernels  from 
a  single  ear.  In  succeeding  years,  a  hundred  or  more  ears  were 
analyzed  from  each  breeding  plot  and  those  ears  from  the  "High 
Protein  Plot"  which  showed  the  highest  per  cent,  protein  were 
saved  to  plant  the  next  year's  "High  Protein  Plot,"  while  those 
ears  from  the  "Low'  Protein  Plot"  which  showed  the  lowest 
per  cent,  protein  were  saved  to  plant  the  "Low  Protein  Plot"  of 
the  next  season.  Like  methods  were  followed  in  the  "High  Oil" 
and  "Low  Oil"  breeding  plots. 

The  results  of  the  "High  Protein"  and  "Low  Protein"  plots 
for  ten  generations  are  shown  in  the  following  table. 

We  have  here  a  concrete  illustration  of  what  was  done  in  ten 
years ;  but  we  must  not  get  from  it  the  idea  that  this  average 
increase  or  decrease  of  protein  in  a  variety  of  white  maize  obtained 
in  ten  years  is  a  measure  of  what  would  be  obtained  by  the 
selection  of  any  other  fluctuation  in  any  other  plant.     This  is 


CONNECTICUT    EXPERIMENT    STATION    BULLETIN    1 58. 


Results  of  Selection  for  Increase  and  DIcrease  of  Protein  in  Maize 
AT  the  Illinois  Agricultural  Experiment  Station.* 


High  Protein  Plot. 
Average  in  per  cent. 

Low  Protein  Plot 
Average  in  per  cent.   ' 

Year. 

Seed  planted. 

Crop. 

Seed  planted. 

Crop. 

between  the 
crops,  per  cent. 

1896 
1897 
1898 

1899 
1900 
I9OI 
1902 
1903 
1904 
1905 
1906 

12.54 
12.49 
13.06 

13-74 
1478 
15-39 
14-30 
15-39 
16.77 
16.30 

10.92 
II. 10 

11.05 
11.46 

12.33 
14.12 

12.34 

13-04 

.  14-98 

14-72 

14.26 

8.96 
9.06 
8.45 
8.08 
7.58 
8.15 
6.93 
7.00 
7.09 
7.21 
1 

10.92 

10.55 

10.55 

9.86 

9-34 
10.05 
8.22 
8.62 
9.27 
8.57 
8.64 

0 

-55 
•50 
1.60 
2.99 
4.07 
4.12 
4-42 
5-71 
6.15 
5.62 

what  was  obtained  under  the  soil  and  cHmatic  conditions  at 
Urbana,  Illinois,  during  a  certain  period  of  ten  years,  when  about 
(in  most  cases)  one  hundred  ears  were  analyzed  and,  on  an 
average,  the  proper,  best  twenty  fluctuations  planted.  The 
amount  of  average  change  that  can  be  made  will  vary  with  the 
number  of  individuals  considered  and  with  the  strictness  of  selec- 
tion. If  one  thousand  ears  had  been  analyzed  each  year  and  only 
five  of  these  planted,  the  same  results  would  have  been  obtained 
in  a  much  shorter  time.  There  are  also  environmental  conditions, 
such  as  moisture,  light  and  available  plant  food  of  the  proper  kind, 
that  would  undoubtedly  influence  the  results.  Moreover,  in 
other  characters  and  in  other  plants  the  variability  of  the  variety 
would  affect  the  progress  that  could  be  made. 

The  next  table  gives  the  results  that  -were  obtained  in  the 
"High  Oil"  and  "Low  Oil"  plots  from  the  same  variety  of  maize 
with  about  the  same  rigidity  of  selection. 

Here  we  see  an  illustration  of  the  point  just  men,tioned :  the 
percentage  changes  in  oil  content,  when  referred  to  the  total  oil 
contents  of  the  crops  are  much  greater  than  the  changes  that  took 
place  in  the  proteids  in  the  same  amount  of  time. 


*  The  figures  for  the  following  three  tables  have  been  furnished 
through  the  courtesy  of  Dr.  L.  H.  Smith,  Assistant  Professor  of  Plant 
Breeding  at  the  University  of  Illinois. 


METHODS   OF    PLANT    IMPROVEMENT. 


49 


Results  of  Selection  for  Increase    and  Decrease  of  Oil  in  Maize  at 
THE  Illinois  Agricultural  Experiment  Station. 


High  Oil  Plot. 

Low  Oil  Plot. 

Aver,  in  per  cent. 

Aver,  in 

per  cent. 

Differences 

Year. 

crops,  per  cent. 

Seed  planted. 

Crop. 

Seed  planted. 

Crop. 

1896 

4.70 

4.70 

0 

1897 

5.39 

4.73 

4-03 

4.06 

.67 

1898 

5.20 

5.15 

3-65 

3-99 

1. 16 

1899 

6.15 

5.64 

3-47 

3.82 

1.82 

1900 

6.30 

6.12 

3-33 

3.57 

2.55 

I9OI 

6.77 

6.09 

2.93 

3.43 

2.60 

1902 

6.95 

6.41 

3.00 

3.02 

3.39 

1903 

6.73 

6.50 

2.62 

2.97 

3-53 

1904 

7.16 

6.97 

2.80 

2.89 

4.08 

1905 

7.89 

7.29 

2.67 

2.58 

4.71 

1906 

7.86 

7-37 

j         2.20 

2.66 

4.71 

There  are  given  in  the  next  table  the  extremes  of  fluctuation  in 
the  ears  analyzed  for  protein  each  season.  It  is  noticeable  that 
several  years  of  selection  passed  before  certain  extremes  appeared, 
as,  for  instance,  the  high  proteid  ear  containing  15.71  per  cent, 
protein  that  appeared  in  the  year  1900.  It  would  be  easy  to  cal- 
culate the  number  of  ears  that  must  have  been  analyzed  the  first 
year  in  order  to  have  had  the  same  relative  probability  of  finding 
an  ear  containing  this  amount  of  protein,  as  there  was  of  obtain- 
ing the  ear  with  13.87  per  cent,  protein  which  was  found  in  that 
year.  Could  there  have  been  a  sufficient  number  of  ears  exam- 
ined and  the  proper  number  planted,  there  is  a  great  probability 
that  these  averages  obtained  in  the  crops  after  ten  years'  breeding 
might  have  been  obtained  in  one  or  two  years.  In  fact,  we  may 
note  here  that  at  this  station  an  ear  of  the  Longfellow  variety 
whose  ancestry  had  been  unselected  was  found,  in  which  the 
protein  content  was  16.2  per  cent.,  which  shows  that  nature  is 
producing  quite  high  extremes  if  we  can  but  find  them. 

But  there  is  a  point  still  more  important.  We  can  see  in  the 
next  table  that  there  is  evidently  a  limit  to  the  fluctuations  in 
protein  or  oil.  The  record-breaking  ears — those  with  extremes 
of  composition  greater  than  had  been  obtained  before  are  fewer 
in  later  years  and  the  extreme  is  not  pushed  up  or  down  to  any 
considerable  extent.  It  seems  evident  tliat  the  isolation  of  the 
extreme  lines  is  fast  being  accomplished,  if  indeed  it  has  not 
already  been  done.     The  curve  of  crop  averages  given  below  will 


50  CONNECTICUT   EXPERIMENT   STATION    BULLETIN    I58. 

Fluctuations  in  Protein  Content  of  Individual  Ears. 


High  Protein  Plot. 

Low   Protein   Plot. 

Year. 

No.  Ears 
analyzed. 

Minimum. 

Maximum. 

No.  Ears 
analyzed. 

Minimum. 

Maximum. 

1896 
1897 
1898 
1899 
1900 
I9OI 
1902 
1903 
1904 
I9OS 
1906 

163 
112 
252 
216 
216 
60 
90 
100 
100 
120 
120 

8.25 
8.34 
7.72 
7.71 
10.31 
8.94 

9-54 

8.47 

10.61 

it).77 

10.46 

13-87 
13.62 
14.92 
14.78 
15-71 
16.12 
15.01 

17-33 
17-79 
17-39 
17-67 

163 
48 
126 
144 
144 
126 
90 
100 
100 
120 
120 

8.25 
8.22 
7-50 

6.66 
7.08 
7.54 
6.37 
6.38 
6.13 
6.62 
6.49 

13-87 
13.98 
16.08 
13.06 
12.29 
1305 
969 
10.20 
10.46 
12.14 
10.91 

show  this  much  plainer.  We  see  that  the  separation  of  the  lines, 
in  both  the  high  protein  and  low  protein  plots,  seems  to  have 
reached  its  limit. 


HIGH  PROT.  PLOT 


LOW  PRQT.  PLOT 


GENERATIONS 


~f?      r.      r;      F3      f;     F,      f;      F,      fg      f^      t7„      f;, 

Fig.  3.     Crop  averages  in  maize  breeding  for  high  and  for  low  protein 
Notice  that  the  curves  are  each  approaching  a  limit — the  horizontal. 

The  important  experimental  data  of  the  constancy  of  either  of 
these  races  has  not  been  determined.  That  is,  it  is  not  known 
what  these  strains  of  maize  with  compositions  made  different 
from  the  average  of  unselected  Burr  s  white  through  selection  of 
extremes,  would  show  in  their  composition  after  several  years 
cessation  of  selection.     But  there  is  no  reason  to  believe  that 


METHODS   OF    PLANT    IMPROVEMENT.  5 1 

these  races  are  more  stable  than  other  improved  races  on  record, 
that  have  been  established  in  the  same  way. 

These  two  cases  of  sugar  beets  and  maize  are  typical  of  all 
improved  races,  whose  improvement  is  due  to  the  selection  of 
fluctuations.  General  selections  to  improve  the  yield  and  quality 
of  our  farm  crops,  such  as  oats,  rye,  potatoes  and  so  on,  all  come 
under  this  head.  Much  good  has  been  accomplished  by  Von 
Lochow  and  Rimpau  in  Germany  in  increasing  the  yield  of  rye 
by  the  use  of  this  method  of  selection,  but  the  process  has  been 
slow  and  must  still  be  continued  from  year  to  year  to  keep  the 
strain  up  to  the  excellence  that  has  been  obtained. 

In  this  country  many  of  the  varieties  of  maize  are  due  to  this 
selection.  It  is  a  common  thing  to  hear  of  these  varieties  that 
have  been  raised  to  a  state  of  comparative  perfection  by  skillful 
breeders,  "running  out"  or  deteriorating  in  the  hands  of  others. 
This  "running  out  of  varieties"  is  largely  a  regression  to  their 
original  types  by  varieties  that  have  been  improved  through  their 
fluctuations.  The  grower  does  not  keep  up  the  selection,  or  the 
variety  is  ill-adapted  to  the  soil  and  climate,  and  deterioration 
is  almost  inevitable.  On  the  other  hand  there  are  varieties,  as 
the  Longfellow,  whose  excellence  is  due  to  desirable  characters 
that  have  been  found  in  nature,  and  have  been  isolated,  and  per- 
petuated. The  greater  constancy  of  these  varieties  is  undoubtedly 
due  to  mutating  characters.  Numerous  constant  hybrid  varieties 
have  also  been  established,  by  combining  the  desirable  characters 
in  two  or  more  of  these  varieties. 

There  are  other  cases  in  which  extreme  fluctuations  can  be 
propagated  with  less  likelihood  of  their  deterioration.  This  is  by 
means  of  bud  propagation.  Seedlings  of  many  fruits  and  of 
garden  plants  can  be  reproduced  by  grafts  or  by  cuttings,  so  that 
their  variation  is  to  a  great  degree  lessened.  There  is  variation 
even  among  grafted  apples  and  peaches,  but  in  general  this  varia- 
tion is  too  small  to  affect  the  qualities  of  "the  fruits  to  a  great 
extent.  What  is  the  amount  of  this  kind  of  fluctuation  as  com- 
pared to  that  of  fluctuation  in  varieties  reproducing  by  seed,  when 
environments  are  comparable,  is  not  known.  We  do  know,  how- 
ever, that  there  is  considerable  variation  in  potatoes  which  are 
propagated  by  buds  (the  tubers).  In  potatoes,  however,  each 
plant  has  a  more  or  less  different  environment,  and  much  greater 
differences  are  to  be  expected  than  with  different  branches  on  the 


5  2  CONNECTICUT   EXPERIMENT    STATION    BULLETIN    I58. 

same  tree.  We  know  that  potatoes  must  be  selected  within  the 
variety  to  keep  them  from  deteriorating,  but  whether  improvement 
can  be  made  by  the  selection  of  their  fluctuations  is  yet  unde- 
termined. 

Isolation  of  Elementary  Species. 

The  improvement  of  our  valuable  field  crops  by  the  isolation 
of  the  best  of  their  elementary  species  has  only  recently  attracted 
attention.  For  the  increasing  prominence  of  this  method,  Nilsson 
and  De  Vries  are  largely  responsible. 

De  Vries  believes  Le  Couteur,  an  English  breeder  on  the  coast 
of  Jersey,  to  have  been  the  first  to  recognize  that  the  cereals  as 
usually  grown  were  full  of  different  types.  In  a  field  of  his 
wheat  twenty-three  distinct  types  were  found.  These  'when 
grown  separately  were  true  "to  type  and  remained  so  generation 
after  generation.  Some  types  were  found  that  were  better  than 
the  average  of  the  mixtures  grown  in  the  fields,  and  some  types 
were  less  productive  and  of  inferior  quality.  A  few  of  the  better 
types  were  isolated  and  multiplied  as  soon  as  possible,  and  put 
on  the  market.  Le  Couteur's  Bellevue  de  Talavera  wheat  is  said 
to  be  still  grown  in  England  and  France,  and  is  reported  to  be  a 
very  uniform  type. 

De  Vries  also  notes  that  the  work  of  Patrick  Shirreff,  the 
Scotch  wheat  grower,  whose  cereal  breeding  has  been  famous 
for  tliree-quarters  of  a  century,  was  the  isolation  of  natural  types 
which  struck  his  eye.  In  his  little  book  entitled  "Shirreff  on 
Cereals"   published  in  1873,  he  says : 

"My  experiences  in  the  improvements  of  the  cereals  arose 
from  the  following  cirpumstance.  When  walking  over  a  field  of 
wheat  on  the  farm  of  Mungoswell,  in  the  county  of  Haddington, 
in  the  spring  of  1819,  a  green  spreading  plant  attracted  my  notice, 
the  crop  then  looking  miserable  from  the  effects  of  a  severe 
winter,  and  the  next  day  measures  were  taken  to  invigorate  its 
growth  by  removing  the  surrounding  vegetation  and  applying 
manure  to  its  roots.  In  the  course  of  summer  several  stalks 
were  cut  down  by  hares;  but  notwithstanding  this  loss  to  the 
plant,  sixty-three  ears  were  gathered  from  it  at  the  harvest,  yield- 
ing 2,473  grains,  which  were  dibbled  in  the  following  autumn  at 
wide  intervals.  For  the  two  succeeding  seasons  the  accumulating 
produce  was   sown  broadcast,   and  the    fourth  harvest  of   the 


METHODS    OF    PLANT    IMPROVEMENT.  53 

original  plant  amounted  to  about  forty-two  quarters  of  grain  fit 
for  seed;  and  proving  to  be  a  new  variety  it  was  named  Mun- 
goswells  wheat." 

Shirreff's  method  of  improvement  was  the  same  as  Le  Cou- 
teur's,  and  they  both  possessed  the  trul  idea  of  selecting  out  ele- 
mentary species.  He  says :  "New  varieties  of  the  cereals  can 
usually  be  obtained  from  three  sources — from  crossing,  from 
natural  sports,  and  from  foreign  countries."  He  seems  to  have  had 
no  idea  of  the  use  of  fluctuations  in  improving  crops.  He  thought 
that  "sports"  or  wide  variations  of  note  should  be  separated  and 
multiplied.  These  he  says,  "usually  breed  true,"  and  when  those 
which  did  breed  true  were  found  to  be  of  value  he  immediately 
set  about  raising  seed  to  supply  the  demand.  During  the  first 
forty  years  he  found  only  four  plants  that  attracted  his  notice, 
and  from  them  he  raised  four  varieties.  After  this  time  he  took 
up  more  systematic  work  in  breeding  and  made  several  valuable 
crosses  among  wheats  and  among  oats. 

More  recently  the  work  which  has  attracted  wide  attention 
throught  its  intrinsic  merit  is  that  of  Dr.  Hjalmar  Nilsson  and  his 
associates  at  the  Swedish  Agricultural  Experiment"  Station  at 
Svalof.  Here  plant  breeding  by  the  Darwinian  idea  of  the  selec- 
tion of  fluctuations  was  tried,  but  was  soon  discarded  because  it 
did  not  give  results.  In  some  cases  improvement  was  made,  but 
even  in  these  instances  the  amelioration  was  slow,  and  was 
inconstant  when  obtained.  Besides,  failures  were  so  numerous 
through  trying  to  force  improvements  in  characters  in  which 
nature  furnished  insufficient  variation,  that  a  surer  method  was 
desired.  • 

A  closer  study  of  elementary  species  or  types  among  the  mix- 
tures of  plants  of  the  cereals,  grasses  and  clovers- as  originally 
grown,  showed  Dr.  Nilsson  that  different  types  were  not  rare  but 
very  numerous,  so  numerous  in  fact,  that  the  present  generation 
would  find  them  entirely  adequate  for  their  needs  if  they  could 
only  give  them  the  minute  study  necessary  to  find  out  their 
differences  and  inherent  qualities.  Such  studies  have  been  and 
still  are  being  carried  out  at  the  Svalof  station  and  by  their  means 
several  new  varieties  of  oats,  wheat,  rye  and  other  plants  have  been 
isolated  and  introduced  to  cultivation.  In  this  country  the  method 
is  being  used  at  several  Agricultural  Experiment  Stations.  The 
Cornell  Agricultural  Experiment  Station  is  separating  the  elemen- 


54  CONNECTICUT   EXPERIMENT    STATION    BULLETIN    158. 

tary  types  of  timothy;  the  Minnesota  Station  has  done  a  large 
amount  of  work  upon  wheat  and  flax;  while  at  the  Connecticut 
Agricultural  Experiment  Station  the  types  contained  in  our 
common  clovers  and  ryes  are  being  studied. 

As  an  example  of  what*  is  to  be  found  in  the  seed  ordinarily 
bought  for  pure  seed  of  our  clovers  and  grasses,  take  the  medium 
red  clover.  The  seeds  vary  in  color  from  white  to  purple.  Some 
of  this  variation  is  due  to  differences  in  maturity  of  the  seeds, 
but  only  a  small  portion  may  be  so  explained.  There  are  types 
with  different  colored  stems.  In  some  the  leaves  have  different 
patterns  of  white  markings ;  while  others  have  plain  leaves  with 
no  markings.  In  some  the  leaves  are  very  hairy,  while  others 
are  nearly  smooth.  Types  are  found  with  leaves  almost  smooth 
at  the  edges ;  others  are  contrasted  with  rather  deep  indentations. 
Some  run  to  foHage,  some  are  profuse  in  blossoms,  and  some 
produce  little  besides  stems.  The  flowers  are  of  different  sizes 
and  colors,  and  the  head  shapes  are  varied.  Nearly  every  varia- 
tion needed  for  commercial  uses  can  be  found  already  produced 
by  nature.  The  general  task  before  the  breeder  in  a  case  of  this 
kind  is  plain.  Individual  heads  from  plants  of  all  these  types 
must  be  grown  in  separate  pedigree  cultures.  Then  the  types 
which  are  suited  to  the  production  of  the  best  quality  of  clover 
hay  are  retained. 

At  Svalof  it  has  been  found  that  the  various  types  of  the  dif- 
ferent grains,  legumes  and  grasses  are  adapted  to  different  uses. 
Some  are  resistant  to  certain  fungous  diseases,  others  are  able  to 
withstand  severe  frosts;  some  are  suited  to  clayey  soils  and 
some  ,to  loose  soils.  In  fact,  the  various  needs  of  the  different 
parts  of  Sweden  are  fast  being  suited  with  particular  types  of 
especially  adapted  plants.  This  is  what  the  breeders  here  must 
strive  to  do.  Connecticut  has  various  types  of  soil  and  a  great 
range  of  climatic  conditions  and  types  should  be  found  to  suit 
these  conditions. 

The  questions  arise:  Are  these  different  types  within  a  sup- 
posedly pure  species  of  cereal,  grass  or  legume,  old  types  per- 
sistent through  a  long  term  of  years,  are  they  still  arising  or  are 
they  mostly  hybrid  forms?  The  experiences  at  Svalof  indicate 
that  yes  must  be  answered  to  all  these  questions.  There  are 
undoubtedly  some  very  old  types  that  have  remained  unnoticed 
and   therefore   unisolated,   but,   nevertheless,    there    is    absolute 


METHODS    OF    PLANT    IMPROVEMENT.  55 

evidence  that  new  types  are  being  continually  produced  in  a  great 
number  of  species.  Many  of  the  types  are  probably  natural 
hybrids,  but  this  does  not  render  them  useless.  They  are  found 
in  ever  increasing  numbers  to  split  up  in  succeeding  generations 
according  to  Mendelian  laws,  and  the  delay  occasioned  in  making 
isolations  is  counterbalanced  by  the  greater  number  of  types  from 
which  to  select  the  needed  ones. 

We  will  summarize  the  distinctions  between  the  selection  of 
fluctuations  and  the  isolation  of  elementary  species  in  the  improve- 
ment of  farm  crops.  In  each  case  we  have  a  field  of  plants 
which  are  supposedly  of  a  pure  and  uniform  variety.  In  reality 
the  field  is  full  of  elementary  species — types  which  are  slightly  but 
distinctly  different  from  each  other.  Some  of  these  types  are 
valuable,  some  are  worthless.  Taken  all  together  they  make  up 
the  average  yield  and  average  quality  that  the  whole  field  shows. 
Each  of  these  types  when  completely  isolated  from  the  mixture 
produces  a  uniform  progeny,  with  of  course  the  usual  fluctuations. 
But  in  the  field  natural  crossing  obscures  many  of  these  types, 
making  the  mixture  still  more  heterogeneous. 

Suppose  we  wish  to  increase  the  yield  of  these  plants  by  the 
Darwinian  method  of  selecting  fluctuations.  We  select  out  a 
dozen  or  more  of  the  best  heads, — say  of  rye.  We  plant  these 
next  year  and  again  select  out  the  best  dozen  heads.  What  have 
we  done?  We  have  in  all  probability  selected  a  mixture  of 
several  types  which  intercross  in  our  breeding  plot.  These  dif- 
ferent types  have  "blood"  of  types  less  productive  in  them.  This 
tends  toward  keeping  up  the  heterogeneity  of  types. — good,  bad 
and  indifferent.  By  continuous  and  very  rigid  selection  we  will 
necessarily  reduce  the  number  of  types  in  our  selected  rye  from 
the  number  in  the  original  rye  with  which  we  started,  but  we  are 
never  certain  of  reaching  our  aim,  particularly  as  the  process  is 
slow.  One  important  reason  for  this  uncertainty  lies  in  the  fact 
that  the  soil  of  a  field  is  never  uniform.  There  are  spots  which 
retain  moisture  a  little  better,  and  places  that  are  a  little  morq 
fertile  than  others.  In  these  places  plants  belonging  to  poorer 
yielding  types  will  do  well  and  are  likely  to  be  selected  in  place  of 
really  better  types  that  have  grown  on  slightly  poorer  ground. 

On  the  other  hand,  in  the  method  of  isolation  of  types  by  pedi- 
gree cultures,  these  objections  are  in  large  measure  overcome. 
All  of  the  types  that  are  in  the  slightest  degree  different  in  their 


56  CONNECTICUT   EXPERIMENT    STATION    BULLETIN    1 58. 

botanical  characters  are  grown  separately.  Some  intercrossing 
between  the  different  types  will  take  place,  but  it  is  much  rarer 
than  is  usually  supposed.  The  types  of  most  of  our  agricultural 
plants  will  remain  fairly  pure  when  a  reasonable  distance  inter- 
venes between  the  plots.  (Maize  is  an  exception,  however,  and 
will  be' treated  separately.)  Some  of  these  types  are  distinct 
natural  types  and  others  are  due  to  crossing.  The  natural  types 
will  remain  distinct  and  true  in  subsequent  generations,  that  is, 
their  botanical  characters  will  remain  true.  Mutations  may  take 
place  and  should  immediately  be  separated  and  Reproduced  in 
pedigree  cultures  by  themselves.  The  hybrid  types  will  split  up  into 
different  types  and  these  should  always  be  isolated.  We  will  then 
have  a  large  number  of  types  whose  characters  remain  distinct  but 
in  which  the  ordinary  fluctuating  variation  will  take  place  due  to 
slight  differences  in  environment.  These  types  will  then  need  to 
be  studied,  and  the  economic  qualities  of  each  noted.  If  a  rye  is 
wanted  that  will  grow  upon  a  light  soil  and  produce  a  large 
amount  of  green  forage  for  soiling,  then  a  number  of  the  types 
should  be  tested  upon  that  kind  of  soil  and  the  best  selected.  If  a 
clover  is  wanted  that  is  resistant  to  frost  and  will  not  winter-kill, 
such  a  type  may  be  found  among  the  large  number  being  tested. 
In  no  case  are  we  trying  to  force  a  variation  along  unnatural 
lines ;  we  take  types  as  nature  has  produced  them,  isolate,  propa- 
gate and  use  them.  In  most  crops  there  is  no  need  for  selection 
other  than  to  obtain  the  necessary  purity  of  type.  The  variety  can 
then  be  propagated  away  from  danger  of  intercrossing  and  put  to 
commercial  use  as  soon  as  sufficient  seed  is  obtained.  Those  crops 
which  possess  characters  whose  high  fluctuations  it  is  desirable  to 
perpetuate,  can  then  be  subjected  to  the  method  of  continuous 
selection. 

Judging  Plants  by  their  Progeny. — There  are  two  important 
methods  used  to  obtain  results  both  in  this  kind  of  breeding  and 
in  the  selection  of  fluctuations.  The  first  is  judging  the^value  of 
a  type  by  the  average  value  of  its  progeny,  and  the  second,  judg- 
ing economic  qualities  by  correlations  with  botanical  characters. 

Judging  the  value  of  a  plant  by  its  progeny  was  introduced* 
independently  by  Hopkins  of  the  Illinois  Agricultural  Experiment 
Station,  Hays  of  the  Minnesota  Agricultural  Experiment  Station 
and  Von  Lochow  of  Germany.  The  principle  has  since  come  to 
be  generally  used  in  breeding  work.     We  can  grow  fifty  to  one 


*This  principle  waS   really  discovered  by  Vilmorin  and  was  used  first  by 
him  on  sugar  beets. 


METHODS    OF   PLANT    IMPROVEMENT.  57 

hundred  seeds  from  a  timothy  plant,  a  wheat  plant  or  an  ear  of 
maize  and  get  a  much  better  idea  of  the  qualities  of  their  mother 
plants  than  if  we  grew  but  one  or  two  seeds  from  each  plant. 
The  seeds  must  of  course  be  grown  in  plots  by  themselves  so  that 
they  can  be  known  to  be  the  progeny  of  a  single  plant.  The 
difficulties  of  non-uniformity  of  environmental  conditions  are  thus 
obviated.     It  is  the  average  in  the  long  run  that  counts. 

Correlated  Characters. — We  have  all  noticed  that  dark  seeds 
among  beans  and  other  crops  are  associated  with  dark  colored 
flowers  or  dark  colored  stems  or  both.  In  some  cases  berries  also 
show  dark  colors  associated  with  dark  colored  flowers.  It  is  clear 
in  these  cases  that  a  certain  amount  of  a  coloring  matter  stored  up 
in  a  seed  gives  it  a  dark  color  which  may  be  increased  and  trans- 
mitted to  other  portions  of  the  plant  which  it  produces.  Such  asso- 
ciations of  character  are  called  correlations.  Many  of  them  have 
been  known  for  years  and  their  causes  are  obvious.  Varieties  of 
sugar  beets  whose  leaves  are  in  open  rosette  form  contain  the 
highest  amount  of  sugar.  This  is  what  should  be  expected,  for 
with  leaves  growing  in  this  form  the  maximum  amount  of  sunlight 
is  possible  for  the  plant,  and  increased  amounts  of  sunlight  make 
possible  increased  amounts  of  sugar.  Hopkins  of  Illinois  has 
shown  that  in  Dent  varieties  of  maize,  kernels  containing  rela- 
tively large  amounts  of  the  translucent  homy  starch  of  the 
endosperm  are  comparatively  higher  in  protein.  This  correlation 
is  explicable  from  the  fact  that  this  part  of  the  kernel  contains  a 
much  higher  per  cent,  of  protein  than  does  the  white  starch 
portion.  In  very  few  cases,  however,  are  the  causes  as  obvious 
as  in  those  just  given. 

De  Vries  states  that  in  France  the  common  stock  is  culti- 
vated in  double-flowered  and  single-flowered  varieties.  As  the 
doubles  produce  no  seed,  seed  to  produce  them  is  saved  from  the 
single-flowered  specimens  of  the  same  variety,  since  such  a  variety 
usually  produces  half  singles  and  half  doubles.  Owing  to  their 
higher  market  price  it  is  advantageous  to  separate  the  doubles 
from  the  singles  as  soon  as  possible.  This  is  done  by  children 
who  are  able  to  pick  out  the  doubles  without  error  when  the  plants 
are  very  small  and  still  without  branches  or  flower  buds. 
De  Vries  says  that  these  differences  in  the  seedling  plants  are  so 
small  that  no  botanist  has  been  able  to  describe  them  but  the  slight 
differences  which  do  occur  are  sufficient  for  the  experienced  eyes 


58  CONNECTICUT   EXPERIMENT   STATION    BULLETIN    1 58. 

of  the  children.  The  same  writer  remarks  that  hyacinth  growers 
are  able  to  distinguish  their  varieties  in  the  bulb,  by  the 
differences  in  size,  in  the  number  of  side  bulbs,  in  form  or  in 
color.  Such  slight  markings  would  mean  nothing  to  the  average 
gardener,  but  the  correlations  of  these  bulbs  with  the  characteris- 
tics of  their  flowers  were  so  familiar  to  the  Dutch  hyacinth 
grower,  Voorhelm,  that  he  is  said  to  have  been  able  to  distinguish 
a  thousand  different  varieties  of  hyacinths  solely  by  examining 
their  bulbs. 

Although  these  correlations  are  evidently  of  different  kinds  and 
probably  of  different  value  to  the  breeder,  but  very  little  work  has 
been  done  concerning  their  classification  and  probable  causes. 
Still  the  breeder  should  not  delay  putting  them  to  use  until  their 
precise  scientific  classification  is  known,  for  all  classes  are 
undoubtedly  of  some  practical  value.  In  biennial  and  perennial 
plants  where  large  numbers  of  seedlings  are  grown  and  possibly  a 
number  of  years  must  elapse  before  the  economic  value  of  the 
fruits  can  be  determined,  any  correlations  which  will  indicate 
those  plants  which  are  absolutely  worthless  are  of  immense  value 
to  the  breeder.  These  plants  can  be  rejected  before  a  great  deal 
of  time  has  been  spent  in  their  care,  leaving  the  ground  which  they 
would  have  occupied  free  for  other  plants.  Likewise  many  com- 
mercial qualities  are  difficult  to  judge,  such  as  the  milling  qualities 
of  grains,  value  of  plant  fibres,  etc.  If  botanical  characters  can 
be  found  which  are  correlated  with  these  qualities,  the  problem  of 
the  improvement  of  such  plants  is  greatly  simplified. 

The  idea  of  the  use  of  correlations  has  assumed  a  much 
greater  importance  since  we  are  but  just  now  learning  the  supreme 
value  of  the  original  choice  in  plant  breeding,  where  the  method 
of  breeding  is  the  isolation  of  elementary  species.  As  these  ele- 
mentary species  when  separated  and  found  of  value  are  to  be 
immediately  multiplied  and  placed  on  the  market,  a  mistake  in  the 
original  selection  leaves  no  room  for  correction;  for  a  continued 
selection  of  fluctuations  by  which  it  is  expected  to  breed  into  a 
variety  qualities  which  it  does  not  naturally  possess,  is  of  no  value. 
The  elementary  species  must  first  be  isolated  and  then  their  agri- 
cultural qualities  tested ;  and  in  these  tests  nothing  can  be  of 
greater  value  than  the  knowledge  that  a  certain  agricultural 
quality  is  correlated  with  a  definite  botanical  character.  The 
breeder  can  then  inspect  his  mixture  of  elementary  species — the 


METHODS    OF    PLANT    IMPROVEMENT.  59 

commercial  variety — and  immediately  separate  the  proper  elemen- 
tary type  which  carries  with  it  the  agricultural  qualities  which  he 
is  seeking.  At  this  point,  after  having  obtained  an  elementary 
species  which  naturally  possesses  a  desirable  quality  as  a  distinct 
heritable  unit  character,  there  are  undoubtedly  many  cases  in 
which  it  is  commercially  profitable  to  use  selection  to  keep  this 
character  up  to  the  highest  limit  in  fluctuation.  Note  that  this  is 
entirely  distinct  from  trying  to  breed  into  a  variety  by  selection  a 
heritable  character  that  it  does  not  naturally  possess. 

It  is  probable  that  many  of  these  correlations  will  be  found 
to  hold  good  only  in  very  narrow  "blood  lines"  of  plants,  and  each 
breeder  of  a  particular  variety  of  our  important  agricultural  plants 
should  make  it  his  duty  to  keep  a  systematic  record  of  all  the 
correlated  characters  which  he  finds.  Such  a  study  will  not  only 
be  productive  of  value  to  the  individual  breeder  in  his  own  special 
field,  but  by  the  general  tabulation  of  such  breeders'  records,  the 
knowledge  of  correlations  might  finally  be  brought  to  such  per- 
fection that  results  in  agricultural  breeding  could  be  obtained  in 
half  the  time  it  requires  at  present. 

The  value  of  correlations  has  been  generally  acknowledged  in 
this  country  and  in  isolated  cases  they  have  been  put  to  use,  still 
they  have  not  been  given  the  amount  of  study  to  which  their 
importance  entitles  them,  and  we  must  look  to  Sweden  as  the 
leader  in  the  practical  utilization.  Nilsson,  at  the  Svalof  station 
less  than  a  decade  ago,  recognized  that  the  study  of  correlations 
would  be  of  the  highest  values  in  the  breeding  of  agricultural 
crops;  and  he  and  his  assistants  have  taken  up  this  work.  Each 
species  of  agricultural  plant  is  carefully  described,  noting  all  the 
differences  that  distinguish  its  elementary  species  and  at  the  same 
time  all  its  economic  qualities.  In  this  way  all  possible  correla- 
tions are  recorded  and  a  careful  study  of  these  tables  has  given 
them  a  large  number  of  ideas  which  they  have  put  to  practical  use. 

As  an  illustration  of  the  results  Nilsson  has  obtained  by  the 
scientific  study  of  correlated  characters,  I  will  give  a  description 
of  his  production  of  the  "Primus"  barley  as  reported  by 
De  Vries.  The  barley  that  is  cultivated  in  the  central  parts  of 
Sweden,  although  of  good  yielding  qualities,  has  a  great 
tendency  to  "lodge,"  through  the  weakness  of  its  stalks.  Nilsson 
selected  the  best  yielding  variety,  the  Chevalier  barley,  for  a 
number  of  years  to  try  to  obtain  stronger  stems,  but  his  selection 


6o  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    1 58. 

of  these  fluctuating  variations  brought  no  results.  Other  varieties 
were  known  with  strong  sturdy  haulms  but  these  were  worthless  as 
to  their  brewing  qualities.  A  careful  study  of  the  botanical  char- 
acters of  the  barley  heads  showed  that  there  was  a  relation  between 
the  form  of  hairiness  to  their  spikelets  and  scales  and  the  com- 
position of  the  grain  which  makes  a  fine  brewer's  barley.  Long 
straight  scales  were  correlated  with  coarse  kernels  but  short  crisp 
wooly  scales  indicated  the  barley  desired  for  the  brewery.  When 
the  fields  of  the  large  coarse  Imperial  barley  with  the  stout  haulms 
were  examined,  out  of  many  thousands  plants  about  sixty  were 
found  with  the  proper  kind  of  short  wooly  scales.  When  these 
were  isolated  and  grown  the  next  season,  certain  of  them  proved 
to  be  an  elementary  species  having  the  strong  haulms  of  the 
Imperial  barley  and  the  fine  brewing  qualities  of  the  best  Chevalier 
varieties.  The  new  variety  was  constant  and  uniform  from  the 
beginning  and  was  multiplied  and  placed  upon  the  market  as  soon 
as  possible,  where  it  now  supplants  the  older  varieties. 

Improvement  by  Hybridisation. 

This  brings  us  to  the  consideration  of  methods  of  hybridization 
as  a  means  of  animal  and  plant  amelioration.  The  modern  use  of 
the  word  hybrid  is  much  broader  in  its  meaning  than  when  used  by 
the  writers  immediately  succeeding  Darwin.  We  shall  apply  the 
term  to  all  individuals  arising  from  crosses  between  elementary 
species,  makirjg  no  distinction  as  to  whether  the  parents  of  these 
individuals  belong  to  different  Linnean  genera,  species  or  varieties. 

The  practical  application  of  artificial  cross- fertilization  to  the 
production  of  new  forms  dates  from  the  beginning  of  the  eight- 
eenth century  when  Thos.  Fairchild,  an  English  gardener,  crossed 
the  carnation  with  the  sweet  william.  The  hybrid  was  almost 
sterile,  but  proving  to  be  a  valuable  variety,  it  was  propagated 
by  cuttings  for  many  years.  This  novelty  seemingly  aroused  little 
enthusiasm  for  the  scientific  study  of  crosses,  and  no  important 
generalizations  were  made  until  about  1760.  At  this  time 
Kolreuter  began  a  systematic  study  of  hybrids,  and  obtained  a 
knowledge  of  their  behavior  that  was  not  greatly  increased  until 
the  last  quarter  of  the  nineteenth  century. 

Kolreuter  established  upon  a  firm  basis  Camerarius'  previous 
discovery  of  the  sexuality  of  plants.  He  also  found  that  hybrid 
plants  resembled  the  pollen  (male)  parent  as  closely  as  they  did 


METHODS    OF    PLANT    IMPROVEMENT.  6 1 

the  seed  (female)  parent.  Further,  that  in  most  cases  it  made 
very  httle  difference  in  the  final  results  of  a  cross,  as  to  which  of 
the  two  parents  was  used  as  the  pollen  and  which  as  the  seed 
parent.  That  is,  the  products  of  reciprocal  crosses  are  nearly 
identical  and  the  male  parent  transmits  as  many  characteristics  to 
the  hybrid  as  the  female  parent. 

Kolreuter,  without  the  apparatus  of  the  modern  microscopist, 
came  very  near  discovering  the  mechanism  of  fertilization.  We 
now  know  that  the  application  of  pollen  grains  to  the  stigma  of 
the  flower's  pistils  is  merely  a  mechanical  act.  The  pollen  grain 
contains  a  minute  structure  "called  the  nucleus,  which  passes  down 
the  style  of  the  pistil  through  the  growing  pollen  tube,  into  the 
ovary,  where  it  unites  with  a  similar  nucleus  in  the  ovule  (fer- 
tilization). F'rom  this  one  cell  the  embryo  in  the  seed  and  later 
the  whole  plant  is  formed  by  exact  and  equal  divisions.  Kolreuter, 
believed  that  fertilization  consisted  in  the  mingling  together  of 
two  vital  fluids,  one  contained  in  the  pollen  and  one  contained  in 
the  stigma,  and  that  th,ese  passing  down  the  style  started  the  ovule 
to  developing  into  the  seed.  He  actually  determined  that  about 
fifty  pollen  grains  were  sufficient  to  mature  at  least  thirty  seeds. 
It  is  marvelous  how  near  the  right  path  he  was,  with  such  limited 
facilities. 

Kolreuter  also  found  that  by  repeatedly  recrossing  a  hybrid  with 
one  of  the  parent  varieties  from  which  it  was  derived,  he  could 
finally  obtain  individuals  that  were  indistinguishable  from  that 
parent  species.  Furthermore,  he  found  that  there  were  excep- 
tional cases  where  reciprocal  crosses  could  not  be  made.  Mira- 
hilis  jalapa  (female  parent)  was  easily  crossed  with  Mirabilis 
longiflora  (male  parent),  but  with  eight  years'  work  he  did  not 
succeed  in  making  the  reverse  cross.  We  now  know  that  a 
reciprocal  cross  is  sometimes  impossible,  because  of  a  seeming 
mechanical  inability  of  the  nucleus  of  the  pollen  to  break  through 
and  gain  admission  to  the  nucleus  of  the  ovule.  When  this 
difficulty  is  artificially  overcome  the  fertilization  is  possible. 

In  the  beginning  of  the  nineteenth  century  we  have  the  work 
of  Thomas  Andrew  Knight,  an  English  plant  physiologist,  who 
has  very  justly  been  called  the  father  of  modern  plant  breeding. 
Knight  was  probably  the  first  who  really  appreciated  the  immense 
possibilities  of  hybridization  as  a  means  of  improving  domestic 
plants,  although  it  is  only  fair  to  state  that  the  principle  of  selec- 


62  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    1 58. 

tion  was  known  and  made  use  of  in  improving  strains  of  cultivated 
plants  by  Joseph  Cooper  of  New  Jersey  at  a  somewhat  earlier 
date.  Kolreuter's  work  was  theoretical,  while  Knight,  in  addition 
to  his  contributions  to  theory,  made  definite  practical  use  of  his 
knowledge  gained  by  experiments.  The  commercial  varieties  that 
he  obtained  through  crossing  were  numerous  and  important. 

Knight's  greatest  contributions  to  knowledge  will  probably 
always  be  known  from  the  two  following  principles  that  he  pro- 
claimed ;  but  science  owes  him  a  still  greater  debt  from  the  fact 
that  he  was  a  pioneer  of  the  type  of  inductive  experiment.  He 
generalized  from  his  experiments  instead  of  making  theories  to 
prove  by  philosophical  discussion.  Knight's  first  principle  was 
that  modification  of  the  food  supply  is  the  leading  cause  of  varia- 
tion. If  we  write  fluctuating  variation  instead  of  variation,  the 
principle  is  still  accepted.  He  also  found  that  the  products  of 
crosses  were  often  more  vigorous  than  the  parents  of  the  hybrid ; 
and  that  a  strain  of  plants  that  had  deteriorated  through  con- 
tinued self-fertilization  could  be  renewed  in.vigor  by  crossing  with 
another  strain.  This  conclusion  has  since  become  known  as  the 
Knight-Darwin  law.  Darwin  supplemented  Knight's  work  by 
many  experiments  comparing  cross- fertilization  with  self-fer- 
tilization and  expressed  his  results  in  this  terse  saying:  "Nature 
abhors  perpetual  self-fertilization."  Darwin's  results,  however, 
rest  on  a  rather  slender  basis.  He^used  characters  such  as  heights 
of  plants  as  a  measure  of  vigor,  and  these  are  far  from  desirable 
standards.  There  are  also  many  cases  known,  such  as  tobacco  and 
wheat,  where  self-fertilization  is  indefinitely  continued  by  nature 
without  evil  results ;  in  fact,  with  them  a  decrease  in  vigor  seems 
to  be  the  immediate  effect  of  a  cross.  The  Knight-Darwin  law 
should  probably  be  changed  to  read :  Nature  resists  any  sudden 
change  in  long  established  conditions. 

During  the  remainder  of  the  nineteenth  century  several  noted 
investigators  into  the  phenomena  attending  hybridization  lived 
and  worked.  Gaertner,  Naudin,  Focke,  Vilmorin  and  many  others 
contributed  large  numbers  of  important  facts,  but  made  no  great 
generalization. 

It  was  found  that  in  general  the  closer  the  botanical  relations 
of  two  plants,  the  more  easily  they  will  cross.  Crosses  between 
varieties  are  generally  very  easy  to  make ;  those  between  Linnean 
species  have  been  made  in  quite  a  number  of  instances,  while 


METHODS    OF    CLANT    IMPROVEMENT.  63 

crosses  between  genera  and  families  are  rare,  although  they  have 
been  recorded.  Close  botanical  relationships,  however,  are  not 
unf,ailing  proofs  of  the  easy  production  of  hybrids ;  Bailey  states 
that  the  squash  absolutely  refuses  to  cross  with  its  near  relative 
the  pumpkin,  while  on  the  other  hand  Focke  mentions  successful 
crosses  between  plants  of  the  lily  and  amaryllisj  and  of  the  figwort 
and  gloxinia  families.  It  was  likewise  discovered  that  hybrids 
arising  from  widely  different  parents  are  usually  much  more 
likely  to  be  sterile  than  are  those  from  nearly  related  parents. 
But  this  rule  is  by  no  means  without  exceptions,  for  a  number  of 
hybrids  between  different  Linnean  species  are  known  that  are 
perfectly  fertile.  Sterility  of  hybrids  among  themselves  does  not 
always  unfit  them  as  prospective  commercial  varieties,  as  they  are 
often  fertile  with  one  or  other  of  their  parents,  and  the  progeny 
of  this  cross  are  fertile  among  themselves.  In  other  cases  infer- 
tile hybrids  can  become  of  great  value  through  propagation  by 
means  of  cuttings,  grafts,  tubers,  etc. 

It  was  also  early  discovered  that  when  two  kinds  of  pollen  were 
placed  on  the  stigma  of  a  plant  at  the  same  time,  only  one  kind  was 
effective  in  the  fertilization.  This  was  called  prepotency  of  pollen. 
It  is  thought  to  be  due  to  the  greater  activity  of  some  kinds  of 
pollen  grains,  since  some  send  out  their  pollen  tubes  faster  than 
others  and  hence  their  nuclei  reach  the  ovule  first.  The  pollen  of 
a  different  variety  is  often  prepotent  over  pollen  from  the  plant 
itself.  In  other  cases,  as  in  the  potato,  the  plant's  own  pollen  is 
prepotent  over  that  of  other  varieties. 

We  can  see  from  the  above  short  account  that  although  many 
experiments  of  merit  were  conducted,  and  quantities  of  isolated 
facts  were  observed  and  recorded,  still  no  great  principle  was 
established  until  the  work  of  Mendel  which  was  described  in 
the  previous  chapter. 

Later  Mendelian  Work. — We  discussed  the  work  of  Mendel 
practically  as  he  left  it.  It  seems  desirable  at  this  point,  after 
having  outlined  the  work  that  can  and  has  been  done  concerning 
fluctuations  and  mutations,  and  the  early  work  in  hybridization,  to 
give  a  few  short  examples  of  the  former  puzzles  that  have  been 
cleared  away  by  extensions  of  Mendelian  principles.  Bateson  and 
his  co-workers  in  England,  Tschermak  in  Austria,  and  Davenport, 
Castle  and  others  in  the  United  States,  are  fast  building  up  a  firm 
foundation  for  the  laws  of  heredity  from  the  impulse  of  Mendel's 


64  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    1 58. 

work.  Experimental  biology  has  had  a  door  of  knowledge 
opened  comparable  to  that  which  Dalton  opened  for  chemistry 
with  his  atomic  theory.  The  work  will  undoubtedly  be  slower 
due  to  its  inherent  complexity,  but  who  shall  say  it  will  not  be 
accomplished  ? 

Previously  we  have  given  explanations  of  Mendelian  phe- 
nomena stripped  of  the  technical  terms  that  have  grown  up  with 
the  increase  of  Mendelian  experiments.  But  in  order  to  prepare 
the  reader  who  may  wish  to  learn  the  latest  extensions  of  the 
theory  as  they  are  published  from  time  to  time,  we  will  explain 
such  terms  as  are  in  constant  use. 

The  cells  whose  nuclei  unite  in  the  process  of  fertilization  are 
called  gametes  or  germ-cells.  When  these  cells  fuse  in  the  pro- 
cess of  fertilization,  a  zygote  is  formed,  and  this  name  has  been 
extended  to  include  the  adult  organism  that  is  finally  formed  by 
the  succeeding  divisions  of  this  cell.  Two  characters  with  con- 
trasting features  which  give  Mendelian  ratios  upon  inter-breeding 
the  product  of  a  cross  are  called  allelomorphs,  and  the  pair  are  an 
allelomorphic  pair.  When  gametes  bearing  similar  allelomorphs 
unite  to  form  a  zygote,  the  product  is  a  homozygote.  For 
example,  the  union  of  two  yellow  colored  peas  forms  a  homozy- 
gote in  regard  to  the  color  character.  When  contrasting  charac- 
ters of  an  allelomorphic  pair  are  united  in  a  zygote,  it  is  called  a 
het  era  zygote:  that  is,  the  crossing  of  a  yellow  and  a  green  pea 
forms  a  heterozygote  for  color. 

We  remember  that  in  cross  breeding  Mendel  believed  that 
contrasting  characters  were  united  in  the  heterozygote,  but  that 
when  this  zygote  produced  gametes  the  two  factors  were  segre- 
gated, fifty  per  cent,  of  the  gametes  bearing  the  character  from 
one  grandparent  and  fifty  per  cent,  from  the  other  grandparent. 
For  example,  a  pea  with  yellow  cotyledons  (Y)  crossed  with  a  pea 
with  green  cotyledons  (G)  produces  a  heterozygote  whose  germ- 
cells  bear  the  characters  Y  and  G  in  equal  proportions.  Mendel's 
view  was  that  these  unit  characters  were  actual  pairs  of  contrast- 
ing characters,  of  which  a  germ-cell  could  possess  but  one. 
Recently  there  has  been  some  doubt  as  to  whether  this  is  the  cor- 
rect hypothesis.  It  has  been  found  that  in  some  cases,- the 
extracted  dominants  or  extracted  recessives,  which  are  the  names 
given  to  the  characters  which  separate  out  apparently  pure  from 
the  cross  and  breed  true, — have  not  entirely  lost  their  possession 


METHODS    OF    PLANT    IMPROVEMENT.  65 

of  the  contrasted  character  but  that  under  certain  conditions  of 
crossing,  the  other  character  may  reappear.  It  seems  that  the 
opposed  character  may  be  contained  by  the  germ-cells,  although 
hidden,  and  may  appear  again  when  conditions  are  right.  What 
these  conditions  are  is  not  known,  but  the  phenomenon  is  quite 
rare,  and  no  fear  need  be  felt  that  it  will  vitiate  numerical  results 
in  practice.  Morgan  has  proposed  the  hypothesis  that  both  char- 
acters are  contained  in  each  germ-cell  but  only  one  of  them  shows 
under  ordinary  conditions ;  that  is,  one  character  or  the  other  by 
chance  obtains  the  mastery  in  the  germ-cell  and  shows  in  the 
organism  to  the  exclusion  of  the  other  character.  It  is  illustrated 
as  follows: 

A(B)  (A)B 

A(B)  (A)B 


iA(B)+2A(B)    (A)B+i(A)B. 


Representing  by  A  the  dominant  character  and  by  B  the  reces- 
sive character,  if  at  some  time  after  making  the  cross  the  A 
character  becomes  the  master  of  half  the  germ-cells  of  both  male 
and  female,  it  may  be  represented  as  A(B).  In  the  other  half 
of  the  germ-cells  the  B  character  obtains  the  mastery  and  the 
cell  may  be  represented  as  (A)B.  Separations  then  take  place 
after  crossing  as  is  shown  in  the  formula.  In  the  first  and  third 
term,  the  free  characters  (the  one  outside  the  parenthesis)  show, 
while  in  the  second  or  hybrid  term,  the  A  character  shows  because 
it  is  thought  to  be  dominant  when  both  A  and  B  are  "free" 
characters. 

Morgan's  proposition  is  that  the  characters  are  not  separated 
in  the  gametes  but  that  the  contrasting  characters  are  both  pres- 
ent but  one  always  in  a  latent  condition  which  can  sometimes 
be  made  patent  by  proper  crossing.  This  view  explains  some  of 
these  exceptional  cases  but  a  larger  number  of  others  are  inexpli- 
cable by  it.  The  view  which  has  so  far  explained  by  far  the 
largest  number  of  cases  is  called  the  presence  and  absence  hypoth- 
esis and  was  propounded  by  Bateson. 

On  this  hypothesis  a  yellow  pea  is  based  on  green;  i.  e.,  the 
yellow  color  is  superimposed  upon  the  green.  The  yellow  pea 
produces  gametes  bearing  two  factors,  one  for  yellowness  (Y) 
and  one  for  greenness  (G).  When  it  is  self- fertilized  or  fertil- 
ized with  another  yellow  pea  a  zygote  is  produced  whose  gametes 


66  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    1 58. 

have  the  formula  YG  but  the  resulting  zygotes  always  have  the 
yellow  color  through  the  presence  of  the  yellow  factor. 

In  the  same  way  the  pure  green  pea  produces  gametes  carrying 
two  factors — one  for  greenness  (G)  and  one  for  absence  of 
yellowness  (y). 

In  cross  breeding  the  yellow  pea  producing  gametes  YG 
would  meet  the  green  pea  producing  gametes  yG  and  the  result- 
ing zygote  will  be  a  yellow  hybrid  whose  constitution  is  YGyG. 
The  hybrid  zygote  would  produce  gametes  YG  and  yG  in  equal 
quantities,  which  meeting  by  chance  upon  self-fertilization  would 
give  the  following  results : 

YG  >  YG 

pollen  YG  ^^  YG  egg 

cells  yG  ^"^   yG  cells 

yG  >   yG 

The  results  would  be  numerically  and,  apparently,  the  same  as 
those  of  the  Mendelian  hypothesis.  Those  zygotes  whose  formu- 
lae are  YGYG  would  be  pure  yellow  superimposed  upon  green, 
those  whose  formulae  are  YGyG  would  be  hybrid  yellow  super- 
imposed upon  green,  and  those  whose  formulae  are  yGyG,  by  the 
absence  of  yellow  (y),  would  be  green. 

We  do  not  know  what  is  the  precise  nature  of  the  absence 
factor  in  the  germ-cell.  Three  hypotheses  have  been  presented: 
there  may  be  (i)  an  actual  substance  representing  absence,  (2) 
there  may  be  literally  nothing,  or  (3)  there  may  be  presence 
but  in  a  latent  state.  The  third  view  is  much  the  same  as 
Morgan's,  but  it  is  open  to  the  objection  that  cases  are  known  in 
which  the  "presence"  factor  is  itself  latent — cases  which- 
Morgan's  theory  would  explain. 

Whatever  is  the  explanation,  it  may  very  well  be  that  these 
pairs  of  unit  characters  represented  by  two  allelomorphs  are 
really  two  pairs  of  characters.  Let  us  recall  that  two  pairs  of 
characters  were  shown  by  Mendel  to  give  four  classes  of  zygotes 
in  the  F^*  generation  in  the  proportions  9 13  13  :i.    Now  if  the  two 


*  Hybridizers  use  the  letter  Fi  (=  ist  filial  generation)  to  represent  the 
immediate  product  of  a  cross.  The  succeeding  generations  arising  from 
the  Fi  generation  are  denoted  by  the  letters  F2,  F3,  etc.  The  parents  of 
the  Fi  generation  are  called  Pi  (='ist  parental  generation),  and  the  grand- 
parents Pa,  and  so  on. 


METHODS    OF    PLANT    IMPROVEMENT.  67 

first  classes  were  indistinguishable  for  some  reason  and  the  two 
last  also  alike,  we  would  have  the  proportion  of  12  to  4,  or  3  to  i. 
Hurst  has  shown  this  to  be  actually  the  case  in  a  large  number 
of  experiments  on  both  plants  and  animals,  and  has  been  able  to 
distinguish  between 'the  different  classes. 

On  crossing  the  Fireball  tomato  (possessing  a  red  flesh  show- 
ing through  a  yellow  skin)  with  the  Golden  Queen  (possessing 
yellow  flesh  showing  through  a  white  skin),  he  obtained  an  F^ 
generation  which  was  exactly  like  the  Fireball,  red  being  domi- 
nant to  yellow.  Upon  self-fertilizing  the  F^  generation  there  was 
a  segregation  in  the  F^  generation  into  reds  and  yellows,  with 
the  expected  Mendelian  ratio  of  three  reds  to  one  yellow.  How- 
ever, there  were  found  to  be  four  distinct  types,  two  reds,  and 
two  yellows.  These  four  types  occurred  in  ratio  of  9:3:3:1  as 
follows :  nine  with  red  flesh  through  a  yellow  skin ;  three  with  a 
red  flesh  through  a  white  skin ;  three  with  yellow  flesh  through  a 
yellow  skin;  one  with  yellow  flesh  through  a  white  skin.  Mr. 
Hurst  thinks  that  it  is  quite  probable  that  the  two  pairs  of 
factors  under  consideration  are  (i)  presence  (R)  and  absence 
(r)  of  red  in  the  flesh,  and  (2)  the  presence  (Y)  and  the  absence 
(y)  of  yellow  in  the  skin ;  presence  being  the  dominant  character 
in  each  case.  The  red  is  superimposed  upon  the  yellow  and  when 
the  factor  for  the  presence  of  red  is  there  the  zygote  is  red ; 
but  when  the  factor  for  the  absence  of  red  is  there  the  zygote  is 
yellow.  The  point  is  that  while  the  red  and  yellow  types  of 
tomatoes  behave  as  Mendelian  characters  with  the  red  dominant, 
there  are  really  four  types  which  can  be  isolated  and  will  breed 
true.  The  conception  of  the  presence  and  absence  factor  may 
be  a  little  puzzling  at  first  but  not  more  puzzling  than  the 
chemists'  physical  conception  of  the  atom.  It  is  as  if  dominance 
were  the  outcome  of  the  presence  of  a  certain  factor,  and  reces- 
siveness  the  result  of  its  absence.  If  we  strip  off  dominance, 
we  have  recessiveness. 

Masked  Characters. — This  construction  of  a  presence  and 
absence  hypothesis  has  been  the  means  of  clearing  up  several 
important  cases  which  at  first  appeared  unconformable  to  the 
Mendelian  ratio.  Hurst  found  upon  crossing  a  pure  bred  "Bel- 
gian Hare"  rabbit  with  a  grey  coat,  with  a  'pure  bred  "White 
Angora"  with  a  white  coat  that  all  of  the  offspring  of  the  F^ 
generation  were  grey.     But  oddly  enough  in  the  F^  generation 


68  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    I58. 

there  appeared  an  approximate  ratio  of  nine  grey,  three  black, 
four  white. 

This  ratio  appears  to  be  due  to  two  sets  of  characters :  a  color 
factor  C  dominant  to  absence  of  color  c,  and  greyness  G  dominant 
to  blackness  b.  The  gametes  of  the  Belgian  Hare  would  have 
the  formulae  (C  +  G),  and  those  of  the  albino  the  formula 
(c-|-b).  The  albino  actually  carries  the  factor  for  black  (b) 
but  the  black  color  is  invisible  because  of  the  absence  of  the 
color  factor  (C).  When  both  C  and  G  are  present,  the  animal 
is  grey;  when  both  C  and  b  are  present  the  animal  is  black. 
But  both  G  and  b  may  be  present  without  the  color  factor  C  and 
the  animal  will  still  be  white.  Moreover,  out  of  the  four  albinos 
produced,  three  carry  the  color  factor  (b)  while  one  is  without 
it.  The  four  albinos  are  alike  in  appearance  and  if  bred  together 
will  give  only  albinos.  But  if  they  are  bred  to  blacks  carrying 
the  color  factor,  it  is  found  that  three  of  the  albinos  carry  either 
a  pure  grey  G  or  a  hybrid  grey  (Gb)  factor,  while  the  other 
carries  only  a  pure  black  factor.  Thus  we  really  have  two 
classes  among  the  albinos  with  the  ratio  of  3:1,  and  instead  of 
the  9 :3  14  ratio  that  appears  to  have  been  obtained,  we  actually 
have  the  true  Mendelian  expectancy  for  two  pairs  of  characters, 
9 :3  :3  :i.  These  cases,  where  two  classes  of  individuals  appear  as 
one  class,  are  called  cases  of  masked  characters. 

The  accompanying  diagram  will  help  elucidate  the  case.  If 
we  represent  color  by  C  (dominant)  and  no  color  by  c  (recessive) 
then  by  crossing  the  two  characters  we  get  an  individual  with  a 
gametic  formula  CCcc  in  the  F^  generation  and  with  self-fer- 
tilization the  ratio  CC  +  ^Cc  +  cc  in  the  F^  generation.  We  will 
represent  these  four  individuals  by  the  four  large  squares  in  the 
diagram.  If  in  the  other  pair  of  characters  greyness  G  is 
dominant  to  blackness  b,  by  crossing  and  then  self-fertilizing 
the  offspring,  we  get  the  ratio  GG  -|-  2Gb  -f-  bb  in  the  F2  genera- 
tion. This  we  represent  by  subdividing  the  four  large  squares, 
for  there  is  an  equal  chance  that  each  of  the  four  classes  repre- 
sented by  the  large  squares  will  fertilize  one  individual  of  each 
of  the  classes  represented  by  the  four  small  squares.  Notice 
that  there  are  nine  squares  criss-crossed  where  C  and  G  both 
are  present ;  these  represent  individuals  with  both  color  and  grey- 
ness present  and  these  individuals  appear  grey.  In  the  three  solid 
squares  color  C  and  no  grey,  or  blackness  b,  are  present  and  the 


METHODS    OF    PLANT    IMPROVEMENT. 


69 


individuals  that  they  represent  are  black;  in  the  four  white 
squares  the  color  factor  C  is  absent  and  the  individuals  that  they 
represent  are  all  albino.  However,  in  thre.e  of  the  albino  squares 
G  is  present,  either  pure  as  GG  or  hybrid  as  Gb ;  these  individuals 
carry  the  grey  color  masked  and  it  can  be  brought  out  by  proper 
crossing.  The  other  albino  carries  the  black  color  b  which  is 
recessive  in  grey,  also  masked,  and  this  too  can  be  brought  out  by 
proper  crossing.  s, 

Reversion. — Another  very  important  phenomenon  that  has 
long  puzzled  hybridists  has  been  found  to  yield  to  a  simple 
Mendelian  explanation.     I  refer  to  the  phenomenon  of  reversion. 


1   1 

1  1 

— 

1 

1 

1 

LLG_ 

(;w 

[^(tI 

Ub 

1 

4c 

c  cc- 

r 

j!c 

Cc- 

K. 

1 '  1 

r> 

cc^Hi 

C'  1 

cJH 

" 

(;■) 

(;hi 

jjm 

^^■■■^1 

' 

;■ 

I 

1  1 

' 

:    GG 

cc 

Gb 
cc 

(t(4 

Gh 

_r> 

c-  Cc 

1 p 

c   Cc^H           cc 
ilB^^H    Gb 

cc 

bb 

(;b 

1   1 

_J||H 

■ 

■ 



1. 

1 

Fig.  4.     Masked  characters 


or  appearance  of  an  ancestral  character  on  crossing.  It  has  long 
been  known  that  by  crossing  two  pure  individuals  that  each  breed 
true  to  a  particular  color ;  individuals  would  sometimes  be  found 
in  the  F^  generation  that  show  the  color  of  a  bygone  ancestor. 
The  phenomenon  is  known  in  both  animals  and  plants  but  is  illus- 
trated nicely  by  the  sweet  pea. 

There  are^itwo  white  varieties  of  the  sweet  pea,  each  of  which 
breeds  true  to  white,  but  Bateson  found  that  upon  crossing,  the  F^ 
generation  are  all  purple.  Then  upon  self-fertilizing  or  inter- 
breeding the  Fi  generation,  nine  purples  and  seven  whites  appear 
out  of  every  sixteen  plants  of  the  Fg  generation.     It  is  clear  that 


70  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    1 58. 

each  race  of  whites  contains  one  factor  necessary  for  the  produc- 
tion of  the  old  ancestral  purple  of  the  sweet  pea,  but  as  neither 
variety  contains  both  factors,  each  breeds  true  to  white  until 
they  are  brought  together.  The  two  factors  are  color  (C)  domi- 
nant to  absence  of  color  (c)  and  purple  (P)  dominant  to  absence 
of  purple  (p)  ;  but  since  one  variety  has  gametes  with  the  formula 
color  plus  absence  of  purple  (C  -|-  p),  it  is  white,  and  since  the 
other  variety  has  the  gametic  formula  purple  plus  absence  of 
color  (P  -f"  c),  it  is  also  white.  If  we  make  use  of  the  same  style 
of  diagram  in  this  case,  using  *CC  +  2Cc  +  cc  to  represent  the 
color  factor  in  the  large  squares,  and  PP  -f-  2Pp  -f-  pp  to  repre- 
sent the  purple  factor  in  the  four  small  squares  of  each  large 
square,  the  matter  is  entirely  clear.     Wherever   P  and  C  are 


"Hi                 1 

-  cn  : :  CE  :  ;  c:    '  uk  ~ 

"On    ~D"0                         ~Q       "D 

rr  rP      -        Pp  Pp 

--  VPVP       — P.Pp 

-  cr        cc      :  cs        cc 

1 

cc        r.c       cc        Cc 

Pp  Pp  -j-       t^p  pp 

--  Pp  Pp            PP  PP 

^c         cc         Cc          CO 

Fig.  5.     Reversion 


present  in  the  same  square  the  individual  is  purple,  but  where 
either  P  or  C  is  absent  (represented  by  p  or  c)  the  individual 
is  white.  There  are  nine  squares  in  which  the  P  character 
brought  by  one  variety  is  in  combination  with  the  C  character 
brought  by  the  other  variet)'  and  these  represent  nine  purple 
individuals.  Likewise,  there  are  seven  squares  in  "Which  either 
the  P  character  or  the  C  character,  or  both,  are  absent;  they 
therefore  represent  white  individuals.  It  is  simply  a  case  where 
the  ratio  of  9:3:3:1  has  the  last  three  terms  combined  and  the 
ratio  is  9:7. 


METHODS    OF    PLANT    IMPROVEMENT.  7 1 

Heterozygotes. — We  have  already  stated  that  dominance  in  a 
complete  form  is  not  universal  in  cases  of  Mendelian  inheritance. 
In  fact  in  possibly  the  majority  of  cases  the  dominant  character 
appears  in  a  diluted  form  in  the  hybrid  progeny  of  a  cross. 
There  are  other  cases  jvhere  the  segregation  of  the  characters 
takes  place  according  to  Mendelian  ratios  but  the  appearance  of 
the  hybrid  is  totally  different  from  either  of  the  parent  types. 
This  class  of  hybrids  has  in  the  past  been  a  stumbling  block  to 
breeders,  because  they  have  tried  to  "fix"  this  character  which 
they  now  know  is  from  its  very  nature  an  impossibility. 

This  is  the  case  with  the  blue  Andalusian  fowl.  No  matter 
how  carefully  this  type  is  selected  and  inter-bred,  poultry  breeders 
have  never  been  able  to  get  it  absolutely  true.  About  half  come 
true  to  the  blue  character,- while  of  the  remainder  one-half  are 
black  and  the  other  half  white  with  black  splashes.  The  very 
fact  that  these  proportions  were  the  Mendelian  expectation  from 
a  cross — i  part  black:  2  parts  blue:  i  part  splashed  white — led 
Bateson  to  believe  that  the  blue  character  was  merely  the  charac- 
teristic appearance  of  the  heterozygote  due  to  the  crossing  of  the 
black  and  the  splashed  white.  This  was  found  by  crossing  to  be 
the  correct  view.  Curious  and  paradoxical  as  it  may  seem,  by 
inter -breeding  the  "pure"  blues  only  one-half  of  the  offspring 
came  blue,  but  by  breeding  together  the  blacks  and  the  splashed 
whites  all  of  the  offspring  were  blue.  These,  however,  split 
into  the  three  classes,  as  would  be  expected,  in  the  next  genera- 
tion. "The  riddle  of  the  impossibility  of  obtaining  a  pure  race 
of  blue  Andalusians  was  thus  solved."  The  very  nature  of  the 
case  showed  that  the  breeders  were  following  a  will-o'-the-wisp. 

There  have  already  been  several  valuable  practical  applications 
of  these  laws  in  problems  of  breeding.  Mr.  R.  H.  Biffen,  in 
England,  has  found  that  susceptibility  and  immunity  to  rust  in 
wheat  are  a  pair  of  simple  Mendelian  characters  in  which 
immunity  is  the  recessive.  He  has  by  this  knowledge  been  able 
to  produce  in  only  three  generations  a  pure  race  of  rust-resistant 
wheat.  Spillman  has  shown  that  the  polled  character  in  cattle 
dominates  the  horned  character,  and  that  by  proper  crossing  a 
polled  race  of  cattle  can  be  established,  with  only  a  single  polled 
mutation  as  foundation  stock.  Thus  when  single  characters  are 
of  supreme  importance,  our  knowledge  of  a  plan  of  action  is  of 


72  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    1 58. 

greatest  value.  We  know  that  we  must  avoid  trying  to  obtain  in 
combination  both  of  a  pair  of  contrasted  characters.  We  know 
that  we  must  breed  for  one  character  at  a  time,  for  by  referring 
to  the  table  on  page  43  we  can  see  that  with  six  pairs  of  characters 
we  must  have  4,096  individuals  to  obtain  one  with  all  six  dominant 
characters  combined. 

It  has  been  stated  that  Mendel's  work  will  make  the  characters 
of  hybrids  as  easy  to  predict  as  are  those  of  chemical  compounds. 
This  is  taking  an  extreme  view  of  the  case.  The  production  of 
hybrids  is  work  of  great  complexity  owing  to  the  great  number 
of  unit  characters  that  make  up  the  higher  plants  and  animals. 
What  we  are  coming  to  know  is  the  most  direct  plan  of  procedure 
in  combining  known  desirable  characters  possessed  by  distinct 
varieties.  Before  predictions  concerning  the  results  of  hybridiz- 
ing can  be  made,  it  must  be  known  for  all  of  our  domestic  plants 
and  animals  what  characters  Mendelize  and  which  of  each  pair 
is  dominant.  There  is  an  enormous  amount  of  work  yet  to  be 
done,  before  we  will  be  able  to  refer  to  a  book  giving  lists  of 
important  characters  of  different  plants  which  will  Mendelize 
together  with  the  characters  which  they  dominate  or  by  which 
they  are  dominated.  Mendel  has  originated  a  new  style  of 
experimental  work, — the  careful  observance  of  individual  charap- 
ters  in  each  of  the  offspring  of  a  'cross.  He  has  brought  con- 
firmatory evidence  that  characters  are  established  fully  formed 
by  mutation,  and  are  inherited  as  such. 

In  conclusion  it  may  be  stated  that  the  general  idea  has  been 
that  it  is  only  hybrids  between  varieties  that  follow  Mendelian 
laws,  but  there  are  already  several  records  of  characters  in  both 
elementary*  species  and  Linnean  species  that  obey  them,  and 
many  more  cases  will  undoubtedly  be  brought  into  conformity 
when  a  larger  number  of  types  have  been  studied. 


*  De  Vries  distinguishes  between  elementary  species  and  varieties,  in 
that  the  elementary  species  of  a  Linnean  species  are  of  equal  rank  and 
usually  differ  from  each  other  in  several  characters,  while  varieties,  he 
says,  are  derived  from  elementary  species  and  differ  from  them  in  ways 
which  are  common  in  a  large  number  of  species.  Varieties,  he  thinks,  are 
less  striking  in  their  differences  and  follow  different  laws  of  inherita.nce 
when  crossed.  This  appears  to  the  writer  to  be  an  arbitrary  distinction, 
and  the  correctness  of  his  conclusions  will  remain  in  doubt  until  more 
light  is  thrown  on  the  question. 


technique  in  plant  breeding.  73 

Technique  in  Plant  Breeding. 

In  the  subject  matter  up  to  this  point,  special  methods  for  the 
improvement  of  particular  crops  have  been  purposely  omitted. 
As  the  work  in  plant  breeding  increases  in  size  and  scope,  methods 
more  or  less  suited  to  each  important  field  crop  will  doubtless  be 
published.  Experiments  are  necessary  to  determine  the  proper 
details  for  such  work.  Many  mistakes  are  to  be  expected,  due 
largely  to  the  complicated  data  from  which  conclusions  must  be 
drawn.  It  is  hoped  that  a  study  of  the  underlying  principles  of 
variation  and  heredity  will  reduce  the  fallacious  proceedings  of 
breeders  to  a  minimum  and  give  them  ability  to  criticize  the 
weak  points  in  the  methods  which  have  been  proposed  for  their 
use.  The  most  important  contributions  to  the  technique  of  breed- 
ing will  probably  be  made  by  those  who,  like  the  Vilmorins  in 
France,  are  well  abreast  with  the  science  of  the  day,  and  yet  who 
regard  the  work  from  its  commercial  side.  The  balance  sheet 
of  any  business  is  a  great  teacher  of  quick  and  direct  methods. 

Although  this  paper  aims  only  to  give  a  short  introduction  to 
the  principles  of  breeding  and  consequently  must  necessarily  omit 
the  discussion  of  the  improvement  of  individual  crops,  still  a  few 
examples  of  technique  in  breeding  will  be  given  in  order  to  make 
clearer  the  explanation  of  the  theoretical  part.  Following  a 
statement  of  the  essential  points  with  which  the  hybridizer  must 
be  familiar,  are  given  (i)  the  important  features  of  breeding  to 
isolate  elementary  species,  using  red  clover,  trifolium  praetense  L. 
as  a  type,  and  (2)  criticisms  of  the  modern  method  of  breeding 
our  most  important  crop,  maize.  The  latter  is  an  example  of  a 
crop  where  both  elementary  species  and  fluctuations  are  dealt 
with  in  practice. 

Flowers  and  their  Parts. 

A  flower  is  said  to  be  complete  when  it  has  calyx,  corolla, 
stamens  and  pistils.  Of  these  the  calyx  and  corolla  are  called 
the  floral  envelopes.  The  calyx  is  the  outer  whorl  of  leaf -like 
parts  of  the  flower,  and  is  usually  green.  The  showy  part  of 
the  flower  is  usually  the  corolla.  The  different  shapes  of  the 
floral  envelopes  in  nature  show  wonderful  adaptation  to  make 


74  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    1 58. 

certain  fertilization  and  hence  to  assure  the  production  of  seed. 
In  artificial  pollination  we  have  to  do  only  with  the  stamens  and 
pistils  which  are  called  the  essential  organs  of  the  flower.  The 
important  feature  of  the  stamen  is  the  pollen  grains.  These  are 
borne  within  the  enlarged  terminal  part  of  the  stamen  called  the 
anther.  When  the  pollen  grains  mature  the  anthers  open  and  the 
pollen  can  then  be  seen  as  a  yellowish  or  brownish  dust.  Each  of 
these  minute  pollen  grains  contains  at  least  one  nucleus  or  essen- 
tial part  of  a  reproductive  cell."  The  pollen  grains  are  the  male 
reproductive  cells  of  the  plant.  The  pistil,  whether  simple  or 
compound,  has  three  parts  when  complete.  The  stigma  at  the 
upper  end  is  generally  rough  or  flattened  or  sticky  in  order  to  hold 
the  pollen  when  it  is  applied.  This  actual  application  of  pollen 
to  the  stigma,  whether  by  insects  or  wind  or  by  the  hand  of  man, 
is  pollination.  When  pollen  grains  are  applied  to  the  stigma,  the 
sticky  substance  upon  the  latter  causes  them  to  grow.  This 
growth  is  called  the  pollen  tube.  It  makes  a  pathway  down 
through  the  style — ^the  slender  part  of  the  pistil — and  finally 
reaches  the  female  or  egg-cell  in  the  interior  of  an  ovule  in  the 
lower  part  of  the  pistil  called  the  ovary.  The  male  nucleus  passes 
down  this  pollen  tube  and  unites  with  the  female  nucleus  in  the 
ovule;  this  process  is  fertilisation. 

Fertilization  in  plants  may  bring  about  a  much  closer  degree 
of  relationship  than  it  may  in  animals ;  fertilization  may  be 
effected  by  pollen  which  was  produced  upon  the  same  flowers  or 
the  same  plant  upon  which  the  ovules  grew.  This  is  self -fer- 
tilisation. Fertilization  by  the  union  of  pollen  and  ovules  which 
grew  upon  dififerent  plants  of  the  same  "pure  line,"  that  is,  sister 
or  cousin  plants,  gives  different  degrees  of  close-fertilisation. 
Union  between  plants  of  different  "pure  lines,"  whether  of  the 
same  or  different  varieties,  is  cross-fertilisation. 

Cross-fertilization  appears  to  be  important  to  a  large  number 
of  plants,  for  there  are  many  devices  in  nature  by  which  cross- 
fertilization  is  effected.  Natural  cross- fertilization  is  effected 
by  water,  wind  and  insects,  although  the  first  agency  is  so  rare 
among  cultivated  plants  that  it  can  be  disregarded.  Wind- 
pollinated  plants  are  called  anemophilous  (wind  loving),  while 
those  pollinated  b)^  insects  are  said  to  be  entomophilous  (insect 
loving). 


TECHNIQUE   IN    PLANT    BREEDING.  75 

Flowers  that  contain  both  stamens  and  pistils  are  known  as 
perfect  or  hermaphrodite  flowers.  A  very  common  means  of 
insuring  cross-fertilization  among  these  plants  is  to  have  the 
stamens  and  the  pistils  mature  at  different  times.  When  the 
stamens  mature  first,  as  in  the  hollyhock,  the  flower  is  pro- 
tandrous;  when  the  pistils  mature  first  the  flower  is  proter- 
ogynous.  Flowers  of  either  of  these  kinds  are  known  as 
dichogamous.  When  flowers  lack  either  pistils  or  stamens  they 
are  said  to  be  incomplete  or  diclinous,  and  are  called  staminate 
or  pistillate  according  to  which  organs  are  present.  When  the 
staminate  and  pistillate  flowers  are  borne  on  the  same  plant,  as 
with  chestnuts,  walnuts,  squashes,  maize  and  others,  the  plant  is 
monoecious.  When  the  different  kinds  are  borne  upon  separate 
plants,  as  willow  and  hemp,  the  plant  is  dioecious. 

The  entomophilous  flowers  are  generally  distinguished  by 
irregular  corollas  which  are  so  adapted  that  insects  visiting 
them  for  nectar  are  almost  certain  to  pollinate  them  with  pollen 
they  have  brushed  from  other  flowers.  The  artificial  pollination 
of  this  class  of  flowers  is  difficult  because  of  the  care  that  must 
be  taken  to  prevent  injury  to  the  essential  organs  while  removing 
the  floral  envelopes  preliminary  to  applying  the  pollen.  There  is 
also  a  class  of  flowers  which  pollinate  themselves  before  opening, 
thus  insuring  self-fertilization.  They  are  called  cleisto gamous 
flowers.  Examples  of  this  class  are  rare,  and  usually  the  same 
plant  bears  flowers  of  some  other  class.  A  careful  examination 
of  the  common  blue  violet  will  show  a  few  inconspicuous  cleis- 
togamous  flowers  down  beneath  the  showy  blue  ones. 

Technique  of  Hybridizing. 

Success  from  artificial  crossing  only  comes  from  close  study 
of  the.  difficulties  attending  the  work,  in  each  particular  case. 
There  are  four  points  with  which  the  operator  must  be  familiar. 

I.  The  natural  habits  of  the  plant  in  its  fertilization.  It  must 
be  known  whether  the  plant  is  diclinous  or  complete ;  and  whether 
the  stamens  and  pistils  mature  at  the  same  or  at  different  times. 
These  facts  will  be  given  in  any  manual  of  botany.  The 
hybridizer  must  find  out  by  experience,  however,  whether  early, 
medium  or  late  flowers  are  the  best  seed  producers,  and  whether 
care  must  be  taken  to  pollinate  sufficiently  at  the  first  application. 


76  CONNECTICUT   EXPERIMENT    STATION    BULLETIN    I58. 

or  whether  several  applications  can  be  made  to  the  same  flower, 
before  the  pistil  falls. 

2.  The  maturity  of  the  pollen.  The  pollen  is  generally  ready 
for  use  when  nature  releases  it  from  the  anthers.  But  in  dif- 
ferent plants  flowers  of  different  times  of  opening  produce  pollen 
in  different  amounts  and  of  different  degrees  of  viability.  In 
some  cases  the  flowers  that  open  first  produce  but  little  pollen  and 
this  unhealthy.  It  may  be  that  in  other  cases  the  late  blossoms 
should  not  be  used.  Healthy  pollen  has  a  regular  shape,  char- 
acteristic of  the  species  or  variety  to  which  it  belongs,  but  when 
examined  under  the  microscope  it  should  always  be  plump. 
Shriveled,  irregular  pollen  of  pure  forms  should  be  discarded. 
It  should  be  recognized,  however,  that  it  is  characteristic  of  many 
hybrids  that  the  ability  to  form  perfect  pollen  is  lessened. 

3.  The  maturity  of  the  stigma.  The  proper  time  for  the 
application  of  the  pollen  to  thp  stigma  varies  from  the  time  of 
the  opening  of  the  flower  in  some  species  until  three  or  four  days 
later  in  others.  An  examination  of  the  stigma  with  a  hand  lens  is 
of  some  value;  for  in  some  types  the  stigmas  are  quite  profuse 
with  a  gummy  exudation  at  the  time  the  stigma  is  most  receptive. 
In  many  types,  however,  experience  alone  will  show  when  to 
make  the  cross.  An  absolute  record  upon  this  point  is  very 
important  for  every  specialist  who  breeds  a  particular  crop,  for 
Hartley  has  shown  that  premature  pollination  is  quite  injurious 
in  cases  of  tobacco,  orange,  cotton  and  tomato  that  he  had 
investigated. 

4.  Prevention  of  pollination  other  than  that  which  is  intended. 
Not  only  must  the  entrance  of  foreign  pollen  be  provided  against,' 
but  in  all  perfect  blossoms,  precautions  must  be  taken  that  self- 
fertilization  is  prevented.  To  prevent  self-fertilization  the 
flowers  must  be  emasculated — that  is,  the  anthers  must  be 
removed — before  the  blossom  opens.  When  the  blossoms  are 
comparatively  large  this  is  easily  done  by  cutting  off  both  the 
corolla  and  stamens  with  a  small  pair  of  surgeon's  scissors. 
If  it  is  in  the  way  the  calyx  also  may  be  removed.  In  case  the 
flowers  to  be  used  are  small,  a  pair  of  very  fine  tweezers  with  the 
points  slightly  flattened  may  be  used.  When  using  tweezers  the 
anthers  should  be  removed  with  considerable  care,  as  they  may  be 
opened  mechanically,  allowing  the  flower  to  self-pollinate. 
When  operating  upon  composites  or  upon  flowers  borne  in  large 


TECHNIQUE    IN    PLANT    BREEDING.  77 

numbers  upon  heads  or  spikes,  most  of  the  flowers  and  flower 
buds  should  be  removed,  leaving  only  three  or  four  individual 
buds  somewhat  isolated  from  each  other.  Each  of  these  should 
then  be  emasculated. 

In  monoecious  or  dicecious  plants,  it  is  of  course  only  necessary 
to  protect  against  foreign  pollen,  as  is  likewise  done  with  complete 
flowers  after  their  preparation  by  removing  the  anthers.  Ordi- 
nary paper  bags  such  as  are  used  by  the  grocer  serve  very  well 
for  protection.  They  should  be  moistened  at  the  end  so  they  can 
be  tied  close  to  the  stem  of  the  emasculated  bud.  In  particularly 
careful  work,  we  should  also  bag  the  pollen  parent,  but  in  com- 
mercial hybridizing  sufficient  pollen  can  usually  be  obtained  by 
shaking  the  flowers  over  a  watch  glass.  There  is  in  this  case  a 
possibility  of  contamination,  but  the  relative  probability  of  it  is 
small.  When  the  stigma  is  receptive,  it  should  be  dipped  in  the 
pollen  if  it  is  available  in  sufficient  amount;  otherwise  it  can  be 
applied  with  a  small  camel's  hair  brush.  After  pollination  the 
flower  should  immediately  be  rebagged,  and  labelled  with  the 
date  and  the  name  of  the  pollen  parent.  After  several  days,  when 
fertilization  has  taken  place,  it  is  better  to  change  the  paper  bag 
to  a  cheese  cloth  bag,  which  will  serve  the  purpose  of  retaining 
the  fruit  should  it  be  dropped,  and  at  the  same  time  admit  light 
and  air. 

In  certain  cases  the  stigmas  of  the  plant  to  be  used  as  the  seed 
parent  are  not  ready  for  some  time  after  pollen  has  been  obtained. 
When  this  happens  the  pollen  should  be  slowly  and  carefully 
dried  under  glass,  then  put  away  in  a  tightly  corked  glass  vial. 
If  the  pollen  is  dried  too  fast,  rapid  evaporation  of  moisture 
causes  the  grains  to  split,  and  the  pollen  is  rendered  useless ;  but 
when  dried  with  care  some  kinds  of  pollen — grapes,  for  instance — 
will  retain  their  vitality  for  a  whole  year. 

Technique  of  Isolating  Elementary  Species. 

In  breeding  field  crops  by  the  isolation  of  elementary  species 
there  are  three  things  to  be  accomplished:  i.  The  separation  of 
the  elementary  species ;  2.  Comparison  of  the  different  types  ; 
3.  Rapid  propagation  of  selected  types  for  commercial  use.  As 
a  typical  example  of  this  kind  of  breeding  we  will  use  the 
experience  of  others  and  ourselves  in  the  breeding  of  our  com- 
mon red  clover,  trifolium  praetense  L. 


78  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    I58. 

The  first  point  to  be  observed  in  separating-  the  natural  types 
of  any  species,  is  to  find  out  the  probabiHty  of  natural  crossing. 
In  maize,  where  large  amounts  of  pollen  are  formed  and  pollina- 
tion is  entirely  anemophilous,  natural  crossing  is  so  great  that 
isolation  of  pedigree  cultures  is  almost  impossible.  In  the  case 
of  smaller  plants  which  commonly  cross  in  nature,  a  framework 
covered  with  very  fine  cheese  cloth  is  placed  over  individual 
plants  from  which  foreign  pollen  is  to  be  kept.  Sometimes  a  few 
humble  bees  are  placed  in  the  tent  to  make  pollination  more 
certain.  This  method  is  often  used  with  choice  plants  of  the  red 
clover,  although  it  has  been  recently  found  that  self-pollination 
is  much  more  common  than  Darwin  supposed.  The  crop  of 
seed  from  a  field  in  which  humble  bees  (their  chief  insect  pol- 
linating agent)  are  common,  is  much  larger  than  the  crop  in  fields 
with  few  of  these  visitors,  but  nevertheless  the  amount  of  self- 
pollination  is  very  considerable,  and  the  separation  of  individual 
plants  by  a  few  feet  of  space  renders  their  isolation  comparatively 
easy  even  without  cloth  screens. 

The  breeder  begins  by  selecting  seed  from  individual  plants 
growing  in  a  mixed  field.  He  also  selects  seeds  of  different 
sizes,  shapes  and  colors  from  the  commercial  product.  These 
seeds  are  planted  in  hills  about  two  and  one-half  feet  each  way. 
The  seeds  of  each  individual  plant  are  planted  in  separate  plots, 
making  the  product  of  each  plot  the  progeny  of  a  single  plant  of 
the  year  before.  Each  of  these  plots  and  each  plant  in  the  plot 
bears  a  separate  number,  which  is  the  means  of  reference  to  the 
description  that  is  always  carefully  kept  of  all  plants  that  are  to 
be  again  propagated.  It  is  only  by  these  minute  descriptions  of 
characters  that  the  different  types  can  be  separated,  for  it  is 
impossible  for  a  breeder  to  keep  in  mind  the  exact  distinctions 
between  types.  When  a  plant  is  found  in  a  plot  that  is  different 
from  the  others,  its  flowers  are  separately  bagged  and  pollinated. 
If  it  appears  worthy  of  further  consideration  its  seed  is  planted 
in  another  plot  the  next  year. 

The  seed  from  each  plot  is  not  mixed  for  planting  the  next 
year's  plot.  If  there  are  different  types  in  a  single  plot,  they 
have  their  seed  saved  separately  and  each  plant  of  a  slightly 
different  type  has  a  different  plot  for  planting  its  seed  in  the 
succeeding  fall.     In  no  case  does  seed  from  more  than  one  plant 


TECHNIQUE    IN    PLANT    BREEDING.  79 

enter  a  plot.  The  breeding  is  distinctly  in-and-in  breeding-,  for 
this  is  the  only  way  in  which  we  can  expect  to  separate  the  types.- 
Of  course  many  of  these  plants  are  rejected  each  year  as 
useless  types,  otherwise  the  work  would  become  too  un\Adeldly  to 
conduct  with  proper  economy  of  time  and  space.  The  remainder 
are  gradually  separated  into  distinct  types  which  reproduce  their 
characteristics  year  after  year,  and  are  then  selected  or  rejected  as 
their  commercial  value  or  uselessness  becomes  apparent.  Varia- 
tions that  we  have  noted,  that  are  of  agricultural  value,  include 
the  following: 

(a)  In  vigor:  some  succumb  to  frost  and  their  usefulness 
comes  to  a  natural  end ;  others  are  resistant  and  come  through  the 
winter  in  the  best  of  shape ; 

(b)  In  stooling:  some  produce  a  large  number  of  stalks; 
others  very  few  ; 

(c)  In  leafiness  :  some  produce  long,  weak  stems,  with  leaves 
only  at  wide  intervals,  while  others  are  remarkable  for  their 
leafiness ; 

(d)  In  character  of  bloom:  some  have  numerous  heads, 
others  few ;  some  beads  are  large,  others  small ;  some  bear  large 
individual  flowers,  others  small ; 

(e)  In  habit  of  growth:  some  are  erect  and  are  easily  cut  by 
the  mower,  while  others  are  recumbent ; 

(f)  In  yield:   the  differences  are  very  marked; 

(g)  In  character  of  stem:  some  are  hard  and  woody,  others 
make  better  hay. 

There  are  many  other  differences  that  serve  to  help  distinguish 
the  types,  but  these  differences  are  in  slight  physical  distinctions 
that  are  probably  of  no  agricultural  value.  It  is  true  that  these 
botanical  marks  may  be  found  to  be  correlated  with  valuable 
qualities  when  they  can  be  more  closely  studied  with  this  idea  in 
view. 

Out  of  all  the  different  types  probably  but  two  or  three  will  be 
found  of  particular  merit.  The  others  must  be  discarded  and 
the  selected  strains  multiplied  for  field  use,  as  rapidly  as  possible. 
The  superior  strains  are  not  mixed  but  each  are  propagated 
separately  as  different  varieties. 

It  is  hoped  before  many  years  we  will  have  varieties  of  each 
of  the  different  forage  grasses  and  legumes,  as  we  now  have 
garden  varieties,  adapted  for  special  purposes.     The  important 


8o  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    1 58. 

way  to  obtain  valuable  improvement  of  such  crops  is  by  isolation 
of  naturally  better  strains  from  their  present  mixtures.  Hybridi- 
zation may  be  necessary  later,  but  at  present  it  is  undesirable  to 
complicate  the  work  until  we  have  accomplished  what  can  be  done 
without  it. 

Technique  of  Maize  Breeding. 

The  breeding  of  maize  or  Indian  corn  is  in  many  ways  quite 
different  from  the  breeding  of  our  other  field  crops.  Maize  is 
the  only  one  of  our  cereals  that  is  monoecious.  The  tassel  con- 
tains the  pollen  or  male  element  while  the  silks  are  the  stigmas  of 
female  flowers.  In  order  that  the  pollination  of  the  silks  shall 
be  relatively  certain,  each  tassel  produces  about  thirty  million 
pollen  grains;  and  as  the  ears  average  considerably  less  than 
five  hundred  grains  apiece,  there  are  about  sixty  thousand  pollen 
grains  produced  for  each  kernel.  With  such  a  large  waste  of 
pollen  floating  about  in  the  air,  there  are  a  great  number  of  inter- 
crosses between  plants  of  the  same  variety.  This  inter-crossing 
has  been  an  obstacle  to  the  improvement  of  maize,  but  it  has  been 
offset  by  the  advantage  over  the  other  cereals,  in  the  possession 
of  large  ears*  Since  each  individual  ear  must  be  handled  and  its 
characters  noted  at  husking  time,  it  is  not  strange  that  ears  with 
desirable  variations  sufficiently  striking  to  catch  the  eye  of  the 
grower,  have  become  the  parents  of  numerous  distinct  varieties. 

It  was  early  learned  that  maize  varieties  inter-crossed  freely 
and  the  lesson  was  heeded  by  the  pioneers  in  maize  breeding.  By 
selecting  seed  ears  toward  a  desired  type  and  by  isolation  from 
other  varieties,  various  strains  have  been  produced  that  are 
remarkably  uniform  in  characters  such  as  color,  that  have 
forcibly  attracted  the  attention  of  the  grower.  Nevertheless, 
even  in  an  isolated  maize  field  grown  from  seed  that  comes  pretty 
true  to  type,  such  as  the  Longfellow  flint  or  the  Reid's  yellow  dent, 
there  are  many  natural  types  grov/ing  side  by  side.  There  are 
stalks  which  bear  their  ears  high  and  there  are  stalks  which  bear 
them  low ;  stalks  with  long  ear  shanks  and  stalks  with  short, 
stalks  with  different  leaf  markings  and  with  notably  different 
tendencies  to  produce  suckers.  The  silks  shade  in  color  from 
purple  to  green  as  do  also  the  tassels.  Differences  are  every- 
where present,  although  those  in  the  ears  themselves  are  the  most 
familiar. 


TECHNIQUE    IN    PLANT   BREEDING.  8l 

A  large  number  of  these  differences  are  due  solely  to  fluctua- 
tions, which  are  more  easily  noted  in  the  large  stalks  and  ears  of 
maize  than  they  are  in  the  smaller  plants  of  cereals  like  wheat 
and  rye.  The  variations  due  to  fluctuations  are  so  large  that  the 
natural  types  are  more  or  less  obscured.  Furthermore,  the 
natural  types  are  in  a  very  mixed  condition  due  to  constant  cross- 
ing with  other  types  by  wind  pollination.  We  have  on  this  account 
a  much  harder  task  than  in  most  plants  to  separate  the  naturally 
productive  types.  Moreover,  after  a  complete  separation  of  such 
types  there  is  still  the  wide  and  valuable  fluctuating  variation  to 
consider ;  for  to  obtain  the  best  results  from  breeding  with  such  a 
large  fruited  plant  as  maize,  the  highest  fluctuations  in  yield  must 
be  constantly  selected  and  perpetuated. 

To  sum  the  matter  up  there  are  these  tasks  before  the  breeder : 

1.  To  isolate  the  best  yielding  and  otherwise  desirable  natural 
types  of  maize  from  the  varieties  in  which  the  "blood"  of  these 
types  is  in  a  chaotic  mixture  with  the  "blood"  of  less  desirable 
types ;  and  to  do  this  in  the  face  of  constant  chances  of  further 
inter-crossing. 

2.  Constantly  to  select  and  propagate  the  highest  fluctua- 
ting variations  of  desirable  characters. 

To  solve  these  two  problems  has  been  the  sole  aim  of  maize 
breeders;  and  has  been  the  means  of  building  up  the  various 
methods  of  maize  breeding  now  in  use  in  the  United  States. 
Each  of  these  methods  has  its  advantages  and  its  disadvantages, 
which  the  writer  will  try  to  discuss  without  bias,  hoping  that  the 
advantages  of  each  may  sometime  be  combined  into  a  more 
perfect  method  than  there  is  at  present.  At  least  it  is  the  right 
of  the  commercial  breeder  to  know  just  what  obstacles  are  in  the 
way  of  the  highest  success;  he  may  then  adjust  a  method  to 
meet  his  own  conditions,  without  being  led  away  by  false  hopes 
of  large  profit  from  blindly  following  the  introducer  of  an 
imperfect  method.  We  leave  out  of  consideration,  because  of 
previous  discussion,  the  fact  that  there  may  be  definite  strong 
points  in  two  varieties  which  it  may  be  desirable  to  combine  by 
hybridization.  This  of  course  should  be  done  when  it  is  desirable, 
but  there  are  probably  natural  types  now  being  grown  that  answer 
all  present  agricultural  purposes  could  we  but  get  from  them 
their  greatest  possibilities.  Even  to  secure  best  results  from 
hybridizing  we  must  start  with  pure  types. 


82  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    1 58. 

In  the  primitive  method  of  selecting  large  ears  from  the  crib, 
the  selections  were  especially  poor  in  point  of  germination;  for 
the  ears  were  not  properly  dried  and  many  of  them  were  partially 
mouldy.  While  this  is  particularly  bad  for  the  yield  in  the  suc- 
ceeding season,  it  has  very  little  to  do  with  the  hereditary  charac- 
ters of  maize.  The  fluctuating  variations  in  the  succeeding 
season  would  be  affected  by  the  weak  diseased  stalks  produced 
by  seed  embryos  with  poor  vitality ;  but  there  is  little  probability 
of  the  weakness  becoming  permanent.  Indeed,  long  continued 
selection  of  this  kind  does  have  quite  an  effect  toward  separa- 
ting a  particular  natural  type  because  the  grower  naturally 
selects  those  ears  that  appeared  to  be  nearest  in  character  to  his 
ideal. 

The  first  improvement  over  this  primitive  method  was  selection 
in  the  fieldjy  The  advantage  of  this  method  over  the  crib  selection 
was  that  the  characters  of  the  plant  which  bore  the  ear  could 
be  taken  into  consideration  as  well  as  the  characters  of  the  ear 
itself.  Hence  progress  in  separating  natural  types  was  much 
faster  than  formerly.  It  was  this  method  that  gave  us  such 
varieties  as  Leaming  and  Reid's  yellow  dent  and  Longfellow  flint 
varieties.  These  varieties,  in  the  hands  of  conscientious  breeders, 
have  been  brought  to  the  most  uniform  type  of  any  varieties 
that  we  possess.  Furthermore,  when  selections  were  made  in  the 
field  more  care  was  naturally  taken  with  the  selected  ears,  which 
ultimately  made  germination  better  and  hence  gave  larger  total 
yields.  Field  selections  were  made  by  the  most  progressive 
growers  as  early  as  the  first  half  of  the  nineteenth  century. 

Not  much  over  ten  years  has  elapsed  since  the  next  step  was 
taken  in  maize  breeding.  This  was  the  introduction  of  what  is 
now  called  the  row  system  of  breeding  made  by  Hopkins  at  the 
Illinois  Agricultural  Experiment  Station.  The  principle  is,  that 
more  definite  idea  of  the  productive  efficiency  of  an  individual  ear 
can  be  obtained  by  getting  the  average  record  of  its  progeny. 
That  is,  when  one  hundred  or  more  hills  are  planted  from  a  single 
ear  and  compared  at  the  end  of  the  season  with  rows  of  equal 
lengths  from  other  ears,  the  weights  of  the  ears  produced  on  each 
row  are  a  more  exact  measure  of  the  productive  efficiency  of 
the  mother  ear  of  that  row  than  are  the  weights  of  one  or  two  of  its 
daughter  ears,  selected  at  random.  The  average  appearance  of  the 
progeny  of  an  ear  is  a  more  correct  index  of  the  productiveness  of 


TECHNIQUE    IN    PLANT    BREEDING.  83 

a  mother  ear  than  is  the  appearance  of  the  mother  ear  itself,  for 
slight  differences  in  soil  fertility,  "moisture  or  sunlight  may 
largely  have  been  the  cause  of  a  superior  looking  ear,  and 
this  superiority  might  not  be  transmitted  to  any  great  degree 
to  succeeding  generations.  In  fact  it  often  happens  that  in 
testing  two  seed  ears,  practically  alike  in  size  and  appear- 
ance, by  this  method,  that  one  yields  at  double  the  rate  of  the 
other.  This  is  a  great  contribution  toward  a  quicker  method 
of  isolating  natural  types,  because  a  row  that  is  exceedingly 
uniform  in  type  growing  from  a  single  mother  ear,  shows 
that  it  (the  mother  ear)  is  less  likely  to  carry  the  blood  of 
numerous  other  natural  types,  than  is  the  ear  from  which  comes 
a  varied  progeny.  Nevertheless,  there  is  in  this  method  the  dis- 
advantage that  in  planting  these  rows  in  the  open  field,  there  is 
a  very  large  chance  of  inter-crossing  between  a  superior  row 
and  an  inferior  row  growing  near  it.  Moreover,  it  is  obviously 
incorrect  to  measure  the  productive  capacities  of  two  rows  grow- 
ing at  opposite  sides  of  a  large  field  on  account  of  very  probable 
inequalities  of  soil.  The  disadvantage  of  inter-crossing  in  the 
row  system  was  to  a  slight  degree  overcome  by  the  United  States 
Department  of  Agriculture,  by  the  introduction  of  a  plot  system 
similar  in  character  to  the  one  previously  described  for  clover. 
Kernels  of  single  ears  planted  together  in  plots  have  the  chances 
for  inter-crossing  with  other  types  minimized,  at  least  for  the 
stalks  growing  toward  the  centre  of  each  plot.  But  the  advantage 
of  this  system  is  offset  by  the  greater  difficulty  of  planting,  har- 
vesting and  keeping  the  records  of  the  progeny  of  the  individual 
ears,  without  making  mistakes  by  which  mixtures  of  other  types 
would  be  introduced. 

It  has  been  suggested  by  the  Ohio  Agricultural  Experiment 
Station  that  the  error  of  comparing  distant  rows  with  each  other 
can  be  decreased  by  the  duplication  of  rows  from  the  same  mother 
ear  in  different  parts  of  the  field ;  while  at  the  Illinois  Agricultural 
Experiment  Station  it  has  been  proposed  to  reach  the  same  end 
by  comparing  with  each  other  only  ears  which  grew  in  one-quarter 
of  the  breeding  plot.  Selections  were  made  of  the  best  rows  in 
each  quarter  of  the  breeding  plot.  Later  the  Ohio  Experiment 
Station  introduced  the  plan  of  planting  so-called  standard  rows 
between  every  five  rows.  These  standard  rows  were  made  b^ 
■planting   in    each   one   a   certain   number   of   kernels    from   the 


84  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    I58. 

same  ears.  The  rows  between  two  of  these  standard  rows  were 
not  compared  with  each  othfer  but  with  the  average  product  of  the 
two  standard  rows  between  which  they  grew.  It  is  evident  that 
it  is  not  desirable  to  perpetuate  these  standard  rows  made  up  of 
composite  samples  of  several  ears.  To  keep  from  doing  this,  in 
the  method  of  continuous  selection,  it  is  necessary  to  detassel  all 
of  these  standard  rows,  thus  preventing  any  possibility  of  pollen 
which  they  had  produced  fertilizing  silks  of  other  rows. 

About  this  same  time  an  extended  experiment  at  the  Illinois 
Station  showed  that  there  were  distinct  effects  from  continuous 
propagation  from  very  .nearly  related  blood  lines  such  as  is 
ordinarily  obtained  in  a  rigidly  selected  breeding  plot.  To 
decrease  this  fault  it  was  suggested  to  detassel  every  alternate 
row  and  to  select  seed  for  the  succeeding  season  only  from  the 
detasseled  rows.  A  plan*  of  planting  was  worked  out  mathe- 
matically by  which  near  relatives  were  separated.  A  breeding 
plot  of  ninety-six  rows  was  grown,  and  every  alternate  row 
detasseled,  leaving  in  all  forty-eight  rows  from  which  seed  might 
be  selected.  These  forty-eight  rows  were  considered  in  four 
quarters  and  four  ears  were  selected  from  each  of  the  six  best 
producing  rows  of  each  quarter.  Of  these  twenty-four  ears 
selected  in  each  quarter,  twelve  were  grown  the  next  season  in 
that  quarter  and  detasseled ;  the  other  twelve  were  taken  to  the 
farthest  removed  quarter  and  grown  the  next  season  in  rows  that 
were  not  detasseled.  In  this  way  the  blood  lines  were  continu- 
ously kept  as  far  apart  as  is  possible  in  an  open  field  breeding  plot. 

It  is  clear  that  while  this  method  lessens  the  evil  effect  of 
inbreeding  and  is  easy  to  manipulate,  it  nevertheless  does  very 
little  toward  isolating  natural  types  because  of  the  selection  each 
year  of  so  many  ears  for  the  next  year's  breeding  plot.  On  the 
other  hand,  the  propagation  of  the  highest  extremes  of  fluctua- 
tions was  brought  to  a  high  degree  of  perfection. 

This  method,  however,  does  contribute  toward  the  slow  isola- 
tion of  the  best  natural. high  yielding  type,  for  the  selection  is 
made  each  year  from  high  yielding  rows,  that  is,  from  the  prog- 
eny of  the  best  mothers,  which  gradually  weeds  out  the  least  pro- 
ductive types.    The  pollen  parents  are  of  course  unknown  although 


**This  plan  is  explained  in  detail  in  Bulletin  No.   152  of  this  station, 
which  will  be  mailed  free  upon  request. 


TECHNIQUE   IN    PLANT   BREEDING.  85 

they  must  be  better  than  the  general  field  average  because  they 
come  each  year  from  the  best  yielding  rows  of  the  previous  sea- 
son; but  there  is  no  way  always  to  guard  against  the  pollination 
of  the  best  detasseled  rows  by  relatively  inferior  tasseled  rows. 
The  influence  of  very  inferior  individuals  or  rows,  however,  is 
guarded  against  by  detasseling  all  weak  and  barren  stalks  as  well 
as  the  regular  detasseled  rows.  Rows  that  produce  a  large  number 
of  undesirable  stalks  are  entirely  detasseled  to  prevent  the  inferior 
blood  of  the  parent  ear  from  being  propagated.  Another  point 
in  which  this  method  is  inefficient  is  that  a  small  number  of 
rows  are  used  in  the  beginning.  If  there  could  be  an  initial  selec- 
tion of  a  very  large  number  of  ears,  there  would  be  a  much  greater 
probability  of  a  final  isolation  of  the  best  types  now  being 
naturally  produced.  The  number  of  ears  planted  in  succeeding 
years  could  be  materially  decreased,  for  the  relative  probability 
of  obtaining  bipod  of  the  best  natural  types  in  the  first  selection 
is  much  greater  than  where  small  numbers  are  used;  and 
having  partially  isolated  these  types  by  the  first  selection, 
it  would  not  be  so  necessary  or  even  desirable  to  continue 
using  large  numbers.  But  even  if  this  were  done,  there 
remains  an  obstacle  in  the  fact  that  even  with  a  large  number 
of  ears  selected  from  the  general  field  for  the  first  breeding  plot, 
there  would  still  be  an  indefinite  number  of  crosses  among  these 
selections ;  that  is,  it  cannot  be  known  what  per  cent,  of  inferior 
blood  there  was  in  the  original  ears  which  were  selected  as  appear- 
ing to  be  the  best.  It  may  be  that  from  this  cause  a  relatively 
pure  ear  of  a  comparatively  ordinary  type  would  show  up  to 
better  advantage  in  a  breeding  plot  than  an  ear  of  a  superior  type 
but  with  a  large  admixture  of  an  inferior  type.  Moreover,  when 
the  selection  is  made  af  the  end  of  the  first  season  from  the  best 
yielding  rows,  there  is  nothing  to  guard  against  these  selected 
ears  having  been  pollinated  from  inferior  rows  in  proximity, 
and  at  this  stage  the  rows  are  all  from  field  selections  with  no 
previous  breeding.  Hand  pollination  is  of  little  practical  use,  for 
we  could  not  tell  definitely  until  harvest  which  rows  would  prove 
the  best  and  a  large  amount  of  tedious  work  would  have  to  be 
done  which  would  ultimately  prove  useless. 

Williams,  of  the  Ohio  Agricultural  Experiment  Station, 
obviates  this  deficiency  by  the  method  he  has  originated.  He 
plants  twenty-five  rows  in  an  ear-to-the-row  test  plot  but  uses  only 


86 


CONNECTICUT    EXPERIMENT    STATION    BULLETIN    I58. 


one-half  of  the  kernels  of  each  ear.  This  test  plot  is  treated  as 
an  ordinary  field  plot  with  no  necessity  of  detasseling  or  remov- 
ing suckers.  The  rows,  however,  are  weighed  at  the  end  of  the 
season  and  compared  with  a  standard  row  which  is  made  up  as 
described  above  (page  83)  and  planted  between  every  five  rows. 
The  remnants  of  the  four  ears  that  have  been  shown  to  possess 
the  greatest  yielding  efficiency  are  planted  the  succeeding  season 
in  two  small  isolated  plots,  detasseling  all  the  plants  grown  from 
one  ear  in  each  plot.  By  saving  the  seed  only  from  the 
detasseled  rows,  a  direct  cross  is  obtained  of  two  of  the  best 
ears  upon  the  other  two  selected  ears.  In  the  third  season  ears 
from  each  of  these  crosses  are  again  crossed  by  planting  in 
alternate  rows  and  detasseling  the  even  numbered  rows.  Each 
year  new  field  selections  are  grown  in  test  plots  and  the  remnants 
of  the  two  ears  which  prove  the  best  are  crossed  the  following 
season.  Finally,  these  are  again  crossed  with  best  ears  from 
previous  crosses.  This  is  continued  indefinitely,  as  is  shown  in 
the  following  diagram. 


I  ST  YEAR 


20  YEAR 


4TH  YEAR       5TH  YEAR 


6THYEAR 


CROP 


Fig.  6.     Williams'  method  of  maize  breeding.     (After  Shamsl.) 


This  method  has'  two  advantages :  it  does  away  with  any  pos- 
sibility of  the  selected  ears  having  been  crossed  during  their 
ear-to-the-row  test  with  pollen  of  inferior  types  and  yet  does  not 
allow  the  strain  to  deteriorate  through  inbreeding.  *  Its  dis- 
advantages are : 


TECHNIQUE   IN    PLANT   BREEDING.  87 

1.  There  is  only  a  small  number  of  ears  in  the  first  breeding 
plot  which  makes  the  chance  of  isolation  of  the  best  types  rela- 
tively small.  This  is  supposedly  obviated  by  taking  the  ears  for 
the  test  rows  each  year  from  the  general  field;  but  the  objec- 
tion to  this  proceeding  is  that  new  mixtures  of  elementary  types 
are  thereby  introduced  into  the  improved  strain.  High  fluctua- 
tions are  thus  continually  brought  into  the  strain,  but  the  isola- 
tion of  the  best  type  is  further  than  ever  frorn  attainment. 

2.  It  is  necessary  to  grow  three  isolated  plots  each  year,  which 
on  many  seedsmen's  farms  is  almost  an  impossibility. 

3.  There  is  not  sufficient  range  for  the  selection  of  fluctuating 
variations  in  such  small  plots,  after  the  individual  ear  crosses 
are  made. 

It  appears,  therefore,  that  there  are  advantages  and  disad- 
vantages belonging  to  each  method,  without  there  having  been 
suggested  a  particularly  desirable  combination  of  the  two.  Where 
there  is  sufficient  uniform  soil  available,  and  where  the  breeder 
is  going  to  devote  his  whole  time  to  the  development  of  maize, 
the  following  method  is  proposed  as  worthy  of  consideration, 
although  it  also  leaves  much  to  be  desired.  In  the  first  year  let 
the  breeder  obtain  select  ears  of  the  variety  from  different 
growers,  of  as  many  different  desirable  types  as  possible.  Let 
these  ears  be  selected  from  standing  plants  where  possible,  pay- 
ing strict  attention  to  the  character  of  the  plants  that  bear  the 
selected  ears.  The  stalks  should  be  firm  and  erect,  with  a  good 
secondary  root  system  and  plenty  of  foliage.  The  ears  should  be 
borne  between  three  feet  six  inches  and  five  feet  high,  on  medium 
length  ear  shanks,  and  should  be  covered  with  only  a  moderate 
amount  of  husk.  They  should  be  mature,  and  should  contain  the 
largest  possible  weight  of  kernels  of  uniform  size  and  shape, 
where  the  time  of  maturity  is  not  an  object.  In  places  where  the 
growing  season  is  short,  smaller  ears  should  be  selected,  but 
from  plants  that  produce  more  than  one  ear,  for  we  have  found 
that  a  pound  of  corn  can  be  produced  by  a  plant  bearing  two 
ears,  in  a  shorter  time  than  a  pound  of  corn  can  be  produced  upon 
a  single  ear.  Other  fancy  score  card  points  need  be  given  little 
attention,  as  what  we  wish  to  obtain  is  a  variety  that  produces  the 
greatest  profit  per  acre.  This  we  shall  find  out  by  actual  test 
without  carrying  into  it  a  preconceived  .notion  of  just  which  type 
is  the  most  productive. 


88  CONNECTICUT    EXPERIMENT   STATION    BULLETIN    1 58. 

At  least  three  hundred  of  these  ears  should  be  planted  in  the 
first  year's  ear-to-the-row  test,  and  five  hundred  or  more  should 
be  grown  if  possible.  These  ears  should  each  be  numbered  and 
only  one-half  of  the  kernels  of  each  planted  in  single  rows  in  the 
test  plot.  Our  object  is  to  have  the  greatest  possible  probability 
of  obtaining  the  best  natural  types  from  the  first  year's  test. 
Notes  should  be  taken  of  the  desirable  or  undesirable  qualities 
shown  by  the  plants  of  each  row,  at  various  stages  of  growth, 
and  at  the  end  of  the  season  each  row  should  be  cut,  husked  and 
weighed  separately. 

All  of  the  corn  from  the  best  fifteen  or  twenty  rows  should  be 
saved  separately  and  the  ears  and  plant  records  of  these  rows 
carefully  studied.  All  rows  whose  products  show  a  number  of 
undesirable  characteristics  should  be  entirely  discarded.  Some 
rows  will  have  shown  a  marked  superiority  over  all  others.  The 
ears  from  those  rows  should  be  examined  minutely  to  see  whether 
they  bear  any  peculiarities  that  may  be  correlated  with  productive 
efficiency.  If  any  such  peculiarities  are  found,  note  them  in  the 
record  book,  for  the  value  of  the  knowledge  of  such  a  correlation 
to  the  breeder  can  hardly  be  estimated. 

The  next  season  plant  the  remnants  of  the  four  ears  that  had 
this  season  produced  the  four  rows  with  the  most  marked 
superiority  over  the  rest.  These  ears  will  possess  the  supe- 
riority shown  in  the  test,  uncrossed  by  inferior  pollen  in  the  test 
plot  to  the  previous  season.  They  will  probably  not  be  distinct 
and  uniform  types,  for  it  is  likely  that  they  contain  blood  of  other 
types  from  previous  natural  crosses  in  the  field ;  but  they  are  the 
pick  of  a  large  number  of  ears,  and  partially  or  wholly  true  to 
type  as  the  case  may  be;  they  are  good  foundation  stock  for  a 
uniform  variety. 

There  are  now  two  methods  of  procedure  open: 

1.  To  begin  at  once  to  select  high  fluctuations,  without  trying 
to  isolate  further  a  single  type. 

2.  To  risk  evil  effect  from  inbreeding  and  work  to  isolate 
further  a  more  uniform  foundation  stock. 

In  the  first  method  the  plan  of  planting  can  be  arranged  by 
planting  in  alternate  rows  with  as  many  combinations  as  pos- 
sible. Then  by  detasseling  the  upper  half  of  each  odd  numbered 
row  and  the  lower  half  of  each  even  numbered  row,  force  as  many 
different  crosses  as  possible  on  these  rows.     Save  the  best  ears  of 


TECHNIQUE    IN    PLANT   BREEDING.  89 

these  crosses  and  begin  a  regular  ear-to-the-row  fluctuation  breed- 
ing* plot  and  continue  it  annually,  using  from  fifty  to  one  hundred 
rows. 

The  second  method  can  be  followed  most  practically  by  planting 
the  remnants  of  the  best  four  ears  in  pedigree  plots.  Each  plot 
is  then  surrounded  by  two  rows  of  some  very  high  growing 
ensilage  corn  planted  one  kernel  every  eight  inches.  These  rows 
are  to  obstruct  foreign  pollen  and  should  be  carefully  detasseled 
each  season.  Personally  I  prefer  to  use  immediately  the  fluctua- 
tion plot  on  account  of  danger  of  continued  inbreeding,  but  I 
am  free  to  confess  that  the  question  is  not  permanently  settled. 
There  may  be  individuals  that  will  stand  continued  inbreeding 
like  Darwin's  morning  glory.  Hero. 

The  point  of  extreme  importance  is  the  advantage  of  isolating 
immediately  from  the  general  field  as  fine  a  foundation  stock  as 
possible.  The  relative  probability  of  doing  this  increases  directly 
with  the  number  of  ears  used  in  the  first  test  plot;  hence  as  large 
a  number  as  possible  should  be  used.  If  we  obtain  a  fine  founda- 
tion stock  we  are  on  the  road  to  success ;  if  we  have  left  the  best 
stock  out  of  our  first  test  plot,  no  amount  of  continued  breeding 
from  the  inferior  stock  can  obtain  it. 

Conclusion. 

These  pages  are  designed  only  to  give  the  practical  plant 
breeder  an  introduction  to  the  theoretical  side  of  his  subject. 
There  are  hundreds  of  agriculturists  who  are  interested  in  the 
work  of  improving  their  important  field  crops,  and  yet  who  know 
nothing  of  the  work  of  their  colleagues  in  the  science  either  pure 
or  applied.  In  many  cases  the  methods  in  use  are  primitive  as 
those  of  several  centuries  past.  In  other  instances  much  impracti- 
cal advice  is  followed  blindly.  We  now  have  plant  breeder's 
associations  in  a  large  number  of  our  states,  as  well  as  a  national 
organizationf  with  over  a  thousand  members,  where  information 
can  be  obtained  upon  special  subjects.  It  is  hoped  that  readers 
of  this  paper  that  expect  to  do  plant  breeding  work,  will  become 
members  of  some  of  these  associations  and  take  up  a  course  of 


*  A  breeding  plo,t  in  which  high  fluctuations  in  yield  are  selected. 

t  The  American  Breeders'  Association.  For  information  address,  Hon. 
W.  M.  Hays,  Secretary,  Washington,  D.  C.  The  Connecticut  Plant 
Breeders'  Association,  Prof.  C.  D.  Jarvis,  Secretary,  Storrs,  Conn. 


go  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    1 58. 

reading  along  the  lines  suggested  in  the  appended  list.  The 
reading  will  be  found  fascinating  as  well  as  instructive  and  the 
association  with  men  interested  in  similar  lines  of  work  will  prove 
to  be  of  great  value. 

The  writer  is  well  aware  that  he  can  be  accused  of  a  pronounced 
De  Vriesian  view  of  this  paper.  He  can  only  plead  that  the 
view  is  from  the  standpoint  of  the  principles  and  theories  that 
give  at  present  the  most  practical  and  efficient  help  in  actual  plant 
breeding.  As  was  stated  in  the  beginning,  the  studies  of  the 
evolution  student  and  of  the  plant  breeder  should  be  and  are 
parallel,  but  only  in  so  far  as  theories  are  proposed  that  can  be 
experimentally  demonstrated.  Experimental  proof  on  all  points 
is  the  ideal  of  the  modern  biologist,  but  it  is  absolutely  essential 
to  the  modern  breeder.  The  philosophical  side  of  biology  can 
have  but  little  weight  with  the  latter.  It  may  be  admitted  that 
certain  forces  may  have  been  of  great  value  in  effecting  an  evolu- 
tion through  eons  of  time,  and  still  be  ineffective  agents  in  the 
time  allotted  to  the  man  who  wishes  to  make  changes  under 
domestication  from  the  standpoint  of  commercial  gain.  It  is 
here  that  the  two  lines  part  company ;  and  it  is  the  plant  breeder 
who  remembers  this  distinction  between  natural  and  artificial 
evolution  when  studying  disputed  theories  of  variation  and 
heredity,  that  will  obtain  the  greatest  aid  from  the  results  of  the 
experimental  biologist.  We  may  admit,  for  instance,  that  the 
believer  in  Lamarckian  factors  as  agents  in  evolution  can  say 
that  experiments  concerning  the  inheritance  of  acquired  charac- 
ters have  been  carried  on  only  for  a  period  of  time  that  would  be 
negligible  in  a  geological  epoch ;  we  may  admit  the  justness  of 
the  same  criticism  of  our  conclusions  regarding  the  ineffective- 
ness of  the  selection  of  fluctuations  in  permanently  changing 
characters :  but  we  are  justified  in  retorting  that  only  such 
theories  can  be  of  use  to  us  that  produce  results  within  the  span 
of  a  human  life.  With  this  point  in  mind  the  writer  believes  that 
a  fair  view  has  been  taken  of  the  questions  touched  upon  in  this 
paper. 

Our  three  main  theses  we  will  again  summarize : 

I.     Organisms  are  composed  of  numbers  of  characters  which 

are  inherited  as  units.     These  units  are  inherited  by  definite  laws 

of  which  Mendel's  law  is  the  first  to  have  been  discovered.    Since 

these  characters  are  inherited  as  units  it  is  most  reasonable  to 


TECHNIQUE    IN    PLANT    BREEDING.  9 1 

suppose  that  each  one  haS  been  originated  fully  formed,  i.  e.,  as 
a  mutation.  The  addition  of  a  new  unit  character  is  the  only  real 
difference  between  this  mutating  organism  and  its  progenitors, 
and  is  the  true  and  only  foundation  for  domestic  improvement. 

2.  The  object  of  hybridization  is  to  shuffle  and  recombine  these 
unit  characters.  Hybridization,  therefore,  actually  produces 
nothing  new  in  spite  of  its  wonderful  manifestations.  Just  as 
chemical  units, — the  elements, — can  be  combined  and  recombined 
into  different  compounds,  so  can  the  unit  characters  of  organisms 
be  combined  and  recombined  by  hybridization. 

3.  The  value  of  the  selection  of  fluctuations  is  slightly  to 
increase  or  to  decrease  the  manifestations  of  a  unit  character 
after  it  has  been  formed  by  nature.  Selection  can  never  produce 
a  unit  character,  for  there  is  obviously  no  basis  upon  which  it 
could  work. 


92  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    1 58. 


,  Reading  List. 

This  list  of  publications  is  suggested  as  a  course  of  supple- 
mentary reading  in  English,  concerning  the  questions  that  have 
been  under  discussion,  and  is  available  to  most  readers  through 
the  public  libraries.  The  reading  should  be  done  cautiously,  for 
it  must  be  remembered  that  most  of  these  publications  were  issued 
previous  to  the  rediscovery  of  Mendel's  work,  in  1900.  If  the 
works  of  De  Vries,  Mendel  and  later  workers  of  the  Mendelian 
school  are  studied  first,  the  reader  will  appreciate  how  great  has 
been  the  change  of  opinion  during  the  last  seven  years  concern- 
ing these  questions,  and  will  not  be  confused  by  the  different 
points  of  view  of  the  early  writers.  The  recent  work  is  scattered 
through  the  files  of  many  journals,  and  is  for  the  most  part  in 
foreign  languages.  For  these  reasons  it  is  not  available  to  many 
readers  and  has  therefore  been  omitted  from  the  list.  To  remedy 
this  omission,  it  is  recommended  that  the  reader  obtain  from  his 
bookseller,  as  soon  as  they  are  published,  the  two  forthcoming 
volumes  on  the  problems  of  variation  and  heredity  by  Wm.  Bate- 
son,  M.A.,  F.R.S.,  Fellow  of  St.  John's  College,  Cambridge. 

Bailey,  L.  H.    Plant  Breeding.    Ed.  4.    N.  Y.     Macmillan.     1906, 

Contains  a  fairly  complete  bibliography  to  the  end  of  1905. 
Bailey,  L.  H.    Evolution  of  oui-  Native  Fruits.    N.  Y.    Macmillan.    1898. 
Gives  a  popular  historical  account  of  the  development  of  American 
varieties  of  fruits. 
Darwin,  Chas.    Cross  and  Self-fertilization  in  the  Vegetable  Kingdom. 
N.  Y.     D.  Appleton. 

Read  chapters  one  and  twelve,  giving  the  plans  of  the  experiments  and 
results. 
Darwin,  Chas.    Animals  and  Plants  under  Domestication.     2  v.     Ed.  2. 
N.  Y.    D.  Appleton. 

The  historical  parts  of  the  first  volunie  are  still  of  great  interest. 
The  theoretical  discussions  in  volume  two  will  only  be  confusing  to 
the  reader  and  had  best  be  omitted.  Our  views  concerning  the  explana- 
tion of  the  phenomena  brought  together  in  volume  one  have  entirely 
changed  since  Darwin's  time. 
De  Vries,  Hugo.  Species  and  Varieties:  Their  Origin  by  Mutation. 
2d  Ed.    Chicago.     Open  Court.     1906. 

A  large  book  which  goes  rather  deeply  into  the  subject.  It  has  in  it 
more  of  interest  to  plant  breeders  than  any  other  book  concerned  with 
evolution. 


READING    LIST.  93 

DeVries,  Hugo.     Plant  Breeding.     Chicago.     Open  Court.     1907. 

A  work  that  is  of  special  interest  to  plant  breeders.     It  should  be 
read  before  the  larger  work.     Gives  an  account  of  Nilsson's  work  in 
Sweden  and  Burbank's  work  in  the  United  States. 
Kellogg,  V.  L.     Darwinism  To-day.     N.  Y.     Henry  Holt.     1907. 

Gives  the  best  summary  of  modern  criticism  of  Darwin.    The  author 
does  not  accept  the  mutation  theory. 
Lock,    R.    H.      Variation,    Heredity    and    Evolution.      London.      John 
Murray.     1906.. 

The  best  popular  presentation  of  the  subject  from  the  modern  view- 
point.    Contains  the  summation  of  important  researches  up  to  1906. 
Morgan,  T.  H.    Evolution  and  Adaptation.     N.  Y.     Macmillan.     1903. 

A  good  criticism  of  Darwin  by  one  who  accepts  the  mutation  theory. 
Punnett,  R.  C.     Mendelism.     Ed.  2.     Cambridge.     Macmillan.     1907. 

A  short  and  readable  account  of  Mendelism  to  date  of  publication. 
Romanes,  G.  J.     Darwinism.     Ed.  3.     Chicago.     Open  Court.     1901. 

An  excellent  account  of  Darwin's  theory  of  natural  selection;    the 
early  criticisms  and  Romanes'  replies. 

The  following  articles,  although  written  without  a  knowledge 
of  Mendelism,  which  would  change  their  statements  to  some 
extent,  are  recommended  as  a  set  of  interesting  papers  that  may  be 
obtained  free  from  any  Congressman  or  from  the  Secretary  of 
Agriculture,  Washington,  D.  C.  Either  the  complete  year  books 
will  be  sent  or  the  separate  articles  may  be  obtained  as  reprints. 

Bailey,    L.   H.     The  Improvement  of   our   Native   Fruits.     Year   book 

U.  S.  D.  A.  1896:   pp.  297-304. 
Hays,  W.  M.    Progress  in  Plant  and  Animal  Breeding.    Year  book  U.  S. 

D.  A.     1901:   ppi  217-232. 
Swingle,  W.  T.  and  Webber,  H.  J.     Hybrids  and  their  Utilization  in 

Plant  Breeding.     Year  book  U.  S.  D.  A.  1897:   pp.  383-420. 
Webber,  H.  J.     Influences  of  Environment  in  the  origination  of  Plant 

Varieties.    Year  book  U.  S.  D.  A.  1896:  pp.  89-106. 
Webber,  H.  J.     Improvement  of  Plants  by  Selection.     Year  book  U.  S. 

D.  A.  1898:   pp.  355-376. 
Webber,  H.  J.  and  Bessey,  E.  A.     Progress  of  Plant  Breeding  in  the 

United  States.    Year  book  U.  S.  D.  A.  1899:  pp.  465-490. 


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